# 2023 Top Data Science Interview Questions - IQCode

### Understanding Data Science: Commonly Asked Interview Questions

Data Science is an interdisciplinary field that involves mining raw data, analyzing it, and identifying patterns in order to extract valuable insights. It encompasses several technologies such as statistics, computer science, machine learning, deep learning, data analysis, and data visualization which are the core foundation of this field.

Over the years, the importance of data has led to the widespread growth of Data Science. Data is considered as the new oil of the future which can be very beneficial if analyzed properly. Data scientists get the exposure to work in diverse domains, solve real-life problems, and make use of trendy technologies. They can drive business and strategic goals, be innovative, and bring out creativity while solving problems.

In this article, we will explore the most commonly asked Data Science technical interview questions for both aspiring and experienced data scientists.

#### Data Science Interview Questions for Freshers

Question 1: What is the definition of Data Science?

`Answer: Data Science is a field of study that involves the extraction of insights from raw data through analysis and mining. It incorporates various fields such as statistics, computer science, machine learning, deep learning, data analysis, and data visualization to accomplish this task.`

### What distinguishes Data Analytics from Data Science?

Data Analytics and Data Science are two related but distinct fields that are often confused with one another. Data Analytics is primarily concerned with the analysis, processing, and interpretation of data to extract meaningful insights. On the other hand, Data Science involves a broader range of activities that go beyond data analysis and include creating predictive models, algorithms, and machine learning applications. In summary, Data Analytics is a subset of Data Science that deals specifically with analyzing data, while Data Science encompasses a wider range of activities related to data analysis and its application in solving complex problems.

```
# Python code example of Data Analytics
import pandas as pd
import numpy as np
```

data = pd.read_csv('data.csv') data.head()

# Data Science example import tensorflow as tf from sklearn.model_selection import train_test_split

(X_train, y_train), (X_test, y_test) = tf.keras.datasets.mnist.load_data() X_train, X_test = X_train / 255.0, X_test / 255.0

### Sampling Techniques and Advantages

In research, there are various sampling techniques utilized such as random sampling, stratified sampling, cluster sampling, convenience sampling, and systematic sampling. The primary benefit of sampling is that it reduces the cost, time, and resources needed to gather data by examining only a portion of the population instead of the entire group. Additionally, sampling provides more reliable results and greater statistical accuracy by providing a representative sample of the population.

### Conditions for Overfitting and Underfitting

Overfitting:

- Training accuracy is high but validation/test accuracy is low
- Model is too complex and has too many parameters for the given dataset
- Model is trained for too many epochs or iterations, causing it to adapt to noise in the training data
- Training data is too small and doesn't represent the true data distribution well enough

Underfitting:

- Both training and validation/test accuracy are low
- Model is too simple and doesn't have enough parameters to capture the complexity of the dataset
- Model hasn't been trained for enough epochs or iterations to converge on a decent solution
- Training data is too noisy or doesn't have enough variation to capture all of the patterns in the data

### Differences between Long Format and Wide Format Data

In data analysis and management, there are two commonly used formats for organizing data: long format and wide format. The main differences between these two formats are as follows:

```
#creating a sample data frame in R to illustrate the differences
library(tidyr)
```

df <- data.frame( id = c(1, 2, 3), name = c("John", "Jane", "Mark"), score.1 = c(85, 92, 76), score.2 = c(80, 90, 85), score.3 = c(91, 89, 83) ) #convert to long format df_long <- pivot_longer(df, -c(id, name), names_to = "score_category", values_to = "score") #convert to wide format df_wide <- pivot_wider(df_long, names_from = "score_category", values_from = "score") #view the original data frame and the converted formats df df_long df_wide

The long format of data is when each row represents a unique observation and each column represents a variable. This format is useful when dealing with repeated measures or multiple groups, where the data can be stacked on top of each other. In the example above, the long format has one row for each combination of id, name, and score category, with a separate column for the score.

The wide format of data is when each row represents a unique subject and each column represents a variable. This format is useful when dealing with simple data sets or when comparing multiple variables across a single subject. In the example above, the wide format has one row for each id and name, with separate columns for each score category.

### Understanding Eigenvalues and Eigenvectors

Eigenvectors and eigenvalues are commonly used in linear algebra and have various applications in data analysis, physics, and engineering. An eigenvector of a square matrix is a non-zero vector that only changes by a scalar factor when the matrix is multiplied by it. The corresponding scalar value is the eigenvalue.

Eigenvectors and eigenvalues are essential in the calculation of principal components in data analysis and in solving differential equations in physics and engineering. They also play a significant role in machine learning algorithms and image processing techniques.

### Meaning of High and Low P-Values

In hypothesis testing, the p-value is the probability of obtaining a test statistic as extreme as, or more extreme than, the observed data under the null hypothesis. A p-value less than the significance level (alpha) indicates that the null hypothesis can be rejected and the alternative hypothesis is supported. Conversely, a p-value greater than the significance level indicates that the null hypothesis cannot be rejected.

Therefore, a high p-value means that there is a high probability of observing the test statistic under the null hypothesis. This suggests that the observed data is not statistically significant and does not provide enough evidence to reject the null hypothesis. On the other hand, a low p-value suggests that the observed data is statistically significant and provides strong evidence to reject the null hypothesis in favor of the alternative hypothesis.

### When is resampling performed?

Resampling is typically performed when data is collected at a certain frequency or resolution and needs to be converted into another frequency or resolution for comparison or analysis. It is also done when trying to fit a model to data with a different frequency or resolution than the model. Resampling can be done in various ways, such as upsampling (increasing frequency or resolution) or downsampling (decreasing frequency or resolution).

### Understanding Imbalanced Data

Imbalanced data refers to a dataset in which one class of data significantly outnumbers another class. This can create problems when training machine learning models, as the model may become biased towards the majority class and perform poorly on the minority class. It is important to address the issue of imbalanced data in order to ensure that the model accurately predicts outcomes for all classes.

### Is there a difference between expected value and mean value?

In statistics, the expected value is a theoretical concept that represents the long-term average of a random variable. On the other hand, the mean value is the arithmetic average of a set of values. Although both concepts involve averaging, they are not necessarily the same.

In some cases, the expected value may not be equal to the mean value. For example, if we toss a fair coin repeatedly, the expected value of the number of heads is equal to half the number of tosses, regardless of the results. However, the mean value will only converge to the expected value as the number of tosses approaches infinity.

Therefore, while the expected value and mean value are related, they are not interchangeable and can sometimes differ.

### Understanding Survivorship Bias

Survivorship bias refers to the flaw in making conclusions or decisions based on a selective set of data that only includes successful outcomes, while ignoring unsuccessful outcomes. It's a tendency to focus on the winners in a particular field and overlook the losers. Survivorship bias can lead to false assumptions about the factors that contribute to success and failure, particularly in fields such as business, investing, and sports. To avoid survivorship bias, it's essential to examine both successful and unsuccessful cases to gain a more comprehensive understanding.

### Definition of Key Terms in Data Analysis

**KPI:** Key Performance Indicator, a measurable value indicating how effectively a company is achieving its key objectives or goals.

**Lift:** A term used in marketing analysis to measure the effectiveness of a marketing campaign. It represents the ratio of the response rate of the targeted group to the response rate of the total population.

**Model Fitting:** A process in statistics that involves adjusting parameters of a model to best fit the observed data. The goal is to find parameters that minimize the difference between the predicted values of the model and the observed or actual values.

**Robustness:** Refers to the ability of a statistical model to work well regardless of changes in the conditions of the data or the assumptions of the model. A model is considered robust if its performance does not deteriorate substantially under various conditions.

**DOE:** Design of Experiments refers to a methodology of conducting a well-structured experiment to identify the relationship of variables that influence a process. The objective is to understand how different factors impinge upon the process to identify ways in which the process can be improved or optimized.

`Acting like API`

### Defining Confounding Variables

Confounding variables are extraneous variables that are not the primary variables of interest in a study or experiment, but can affect the outcome of the study. They may introduce errors, biases or false associations in the results. It is important to identify and control for confounding variables in order to accurately assess the relationship between the primary variables and the outcome of interest. This can be done through careful study design, statistical analysis, and/or randomization.

### Definition and Explanation of Selection Bias

Selection bias refers to a situation in which a sample or group of participants is not representative of the true population being studied. This may occur when the sample is selected in a way that is not random, or when certain groups are excluded from the sample.

For example, if a study on the effectiveness of a new drug only includes participants who are already known to respond well to medication, the results may not accurately reflect how the drug will work for the general population. This is because the sample is biased towards individuals who are more likely to respond positively to medication.

Selection bias can occur in many different types of studies, including surveys, experiments, and observational studies. It is an important consideration when interpreting research findings, as biased samples can lead to inaccurate conclusions and recommendations.

### Bias-Variance Trade-off

The bias-variance trade-off is a principle in machine learning that refers to the relationship between a model's ability to fit the training data and its ability to generalize to new data. A model's bias measures its tendency to consistently deviate from the true value of the target variable, while its variance measures its sensitivity to changes in the training data. As such, a high bias model will tend to underfit the training data, while a high variance model will tend to overfit the training data. The ideal model is one that finds the right balance between bias and variance, leading to good generalization performance on new data.

### Definition of Confusion Matrix

A confusion matrix is a table used in the field of machine learning to evaluate the performance of a classification model. It shows the number of correct and incorrect predictions made by the model compared to the actual outcomes (or ground truth) in the dataset. The matrix is constructed with actual values as columns and predicted values as rows, which allows the user to easily calculate various metrics such as accuracy, precision, recall, and F1 score.

### Explanation of Logistic Regression and Recent Usage Example

Logistic Regression is a statistical method used for modeling the relationship between a binary dependent variable and one or more independent variables. It is commonly used to predict the probability of an event occurring based on given data.

As an example, I recently used logistic regression in a marketing project to predict the likelihood of customers buying a certain product based on their age, gender, income, and location. By analyzing the data and using logistic regression, we were able to identify the key factors that influenced customer purchasing behavior and improve our marketing strategy accordingly.

```
# Sample Python code for Logistic Regression
from sklearn.linear_model import LogisticRegression
from sklearn.model_selection import train_test_split
from sklearn.metrics import accuracy_score
# Load the dataset
data = pd.read_csv('customer_data.csv')
# Split the data into training and testing sets
X_train, X_test, y_train, y_test = train_test_split(data[['age', 'gender', 'income', 'location']], data['purchase'], test_size=0.3, random_state=42)
# Create and fit the logistic regression model
model = LogisticRegression()
model.fit(X_train, y_train)
# Make predictions on the testing set
y_pred = model.predict(X_test)
# Calculate the accuracy of the model
accuracy = accuracy_score(y_test, y_pred)
print("Accuracy: ", accuracy)
```

### Overview of Linear Regression and Its Major Drawbacks

Linear regression is a commonly used statistical technique that is used to model the relationship between a dependent variable and one or more independent variables. The aim of this technique is to find a linear relationship between the dependent variable and the predictor variables, which can help in predicting future outcomes.

Despite its popularity, there are several major drawbacks to using the linear model. One of the major drawbacks is that it assumes a linear relationship between the dependent variable and the predictor variables, which may not be the case in reality. Additionally, it is also sensitive to outliers, which can significantly impact the model's predictions. Furthermore, it assumes that the residuals (i.e., the difference between the observed value and the predicted value) are normally distributed and have constant variance, which may not be true for all datasets.

Other limitations of linear regression include its inability to handle non-linear relationships, the assumption of independence between observations, and the inability to capture interaction effects (i.e., the effect of one predictor variable on the dependent variable may depend on the value of another predictor variable).

`<!-- sample code here -->`

### Understanding Random Forest and How it Works

Random Forest is a type of machine learning algorithm that can be used for both classification and regression tasks. It is an ensemble learning method that combines multiple decision trees to improve the accuracy of predictions.

In a Random Forest, a large number of decision trees are created using a randomly selected subset of features and training data. Each tree is trained using a subset of training data, and at each node in the tree, only a subset of features is considered for splitting.

When making a prediction, the Random Forest algorithm aggregates the prediction results from all the decision trees to arrive at the final prediction. This helps to reduce the risk of overfitting, a common problem with individual decision trees.

One of the main advantages of Random Forest is that it can handle large datasets with high dimensionality. It is also relatively easy to tune the parameters of the algorithm to achieve optimal results for a given problem.

Overall, Random Forest is a versatile and powerful machine learning algorithm that can be used for a wide range of tasks, including image analysis, natural language processing, and predictive modeling.

### Finding the Probability of Seeing Shooting Stars

In a 60-minute interval, there are 4 sets of 15 minutes. Therefore, the probability of not seeing a shooting star in a 15-minute interval is 0.8. The probability of not seeing a shooting star in all four intervals is (0.8)^4 = 0.4096.

Therefore, the probability of seeing at least one shooting star in an hour is 1 - 0.4096 = 0.5904 or 59.04%.

### Understanding Deep Learning and its Difference from Machine Learning

Deep learning is an advanced subset of machine learning that involves the use of neural networks to train a machine on a large set of data in order to recognize patterns and make predictions. The main difference between deep learning and machine learning is that deep learning algorithms have many layers of artificial neural networks that can perform complex tasks by themselves.

On the other hand, machine learning algorithms require human intervention to find the right features or data representations to learn from. Additionally, deep learning is capable of processing massive amounts of data faster and more accurately than traditional machine learning algorithms.

`// Sample code for deep learning using TensorFlow framework`

```
import tensorflow as tf
from tensorflow import keras
model = keras.Sequential([
keras.layers.Flatten(input_shape=(28, 28)), # Input layer
keras.layers.Dense(128, activation='relu'), # Hidden layer
keras.layers.Dense(10, activation='softmax') # Output layer
])
model.compile(optimizer='adam',
loss='sparse_categorical_crossentropy',
metrics=['accuracy'])
```

The above code shows a basic implementation of a deep learning model using the TensorFlow framework. This model consists of an input layer, a hidden layer, and an output layer, each with different activation functions. The model is then compiled with an optimizer, a loss function, and accuracy metrics in order to train it on data and improve its performance over time.

### Understanding Gradient and Gradient Descent

Gradient refers to the slope of a function. In machine learning, it is used to calculate the direction and magnitude of the steepest slope of a loss function with respect to the model's parameters. Gradient descent is an optimization algorithm that is used to update the model's parameter values in the opposite direction of the gradient to minimize the loss function. By repeatedly calculating the gradient and adjusting the model's parameters, the algorithm finds the optimal set of parameter values that minimize the loss function. Gradient descent is commonly used in various machine learning algorithms such as linear regression, logistic regression, and neural networks.

### Time Series vs Regression Problems in Data Science Interviews

In a data science interview for an experienced position, you may encounter the question: "How are time series problems different from other regression problems?"

Code:

In time series problems, the data is collected over time, making it a sequence of observations with a temporal relationship. On the other hand, regression problems involve predicting a continuous output variable from one or more input variables without any temporal component.

Additionally, time series data is often non-stationary, meaning that its statistical properties such as mean and variance change over time, which makes it challenging to model accurately. In regression problems, the assumption is that the data is stationary.

Finally, the evaluation metrics are different for time series and regression problems. In time series, we use metrics such as mean absolute error (MAE) and mean squared error (MSE) over time, while in regression problems, we use metrics like R-squared and mean squared error (MSE) in cross-validation.

### Explanation of RMSE and MSE in Linear Regression

In Linear Regression, Mean Squared Error (MSE) and Root Mean Squared Error (RMSE) are two commonly used metrics to evaluate the accuracy of a machine learning model. Both of these metrics are used for measuring the difference between the actual and predicted values of the target variable.

MSE is the average of the squared differences between the actual and predicted values of the target variable. Root Mean Squared Error (RMSE) is the square root of the MSE. In other words, RMSE is the standard deviation of the residuals of the predictions.

Both MSE and RMSE are used to measure the error of a regression model, with lower values indicating better performance. RMSE is generally preferred as it gives a better measure of the magnitude of the error.

The formulas for calculating MSE and RMSE are as follows:

`MSE = 1/n * ∑(y_true - y_pred)^2`

`RMSE = sqrt(MSE)`

Where `n` is the number of observations, `y_true` is the actual or observed value, and `y_pred` is the predicted value.

### Explanation of Support Vectors in Support Vector Machines (SVM)

Support vectors are the data points in a support vector machine (SVM) algorithm that help to define the hyperplane that best separates the classes in a classification problem. These data points lie closest to the decision boundary, also known as the maximum margin hyperplane. The support vectors are used to calculate the distance between the hyperplane and the other data points. Any data points outside of the margin boundaries do not contribute to the construction of the hyperplane. The goal of a SVM algorithm is to maximize the margin between the support vectors and the decision boundary, while minimizing misclassifications.

### Training a Machine Learning Model on a Low-RAM Laptop

If you have experience in Machine Learning and Data Science, you may encounter a situation where your laptop RAM is not sufficient for the size of the dataset that you want to train your model on. For example, if your laptop’s RAM is only 4GB and you want to train your model on a dataset of 10GB, you may face memory issues.

To overcome this issue, you can consider the following options:

1. Use a cloud-based virtual machine (VM) or a remote server with high RAM capacity, such as Amazon EC2 or Google Cloud Compute Engine, to train your model.

2. Use a smaller sample of the dataset for training the model. However, this may result in lower accuracy and generalization of the model.

3. Use a technique called mini-batch learning, where you split the dataset into smaller subsets (batches) that can fit into the RAM. You can train the model on each batch and update the weights of the model incrementally.

4. Use dimensionality reduction techniques to reduce the size of the dataset without losing too much information.

By using these techniques, you can train your machine learning model even on low-RAM laptops.

### Neural Network Fundamentals Explained

A neural network is a type of machine learning model that is inspired by the structure and function of the human brain. It is composed of layers of interconnected nodes, or “neurons,” which process and transmit information.

The fundamental building block of a neural network is the neuron, which takes in one or more inputs, multiplies them by weights, and then applies an activation function to produce an output. The activation function determines whether the neuron “fires” or not, based on whether the input exceeds a certain threshold.

Neurons are organized into layers, with each layer processing a different aspect of the input data. The input layer receives the raw data, which is then passed through one or more hidden layers to produce an output. The output layer provides the final prediction or classification.

Training a neural network involves adjusting the weights and biases of the neurons to minimize the error between the predicted output and the actual output. This is typically done using a technique called backpropagation, which calculates the gradient of the error with respect to each weight and updates the weights accordingly.

Neural networks can be used for a variety of tasks, including image classification, speech recognition, natural language processing, and time series prediction. They have achieved state-of-the-art performance on many benchmarks and are widely used in industry and academia.

### What is a Generative Adversarial Network?

A Generative Adversarial Network (GAN) is a type of deep learning framework where two neural networks, namely the generator and the discriminator, work together to create realistic outputs that resemble a training dataset. The generator creates synthetic data samples while the discriminator evaluates the authenticity of these samples. Through iterations of training, both networks improve until the generator produces data that is indistinguishable from the real data set it was trained on. GANs have been successful in generating images, videos, and other types of data.

### What is a Computational Graph?

A computational graph is a directed graph that represents mathematical and logical operations performed in a machine learning model. It consists of nodes that represent variables and operations, and edges that represent the flow of data between them. Computational graphs are commonly used in deep learning to optimize and train neural networks. By representing a model as a computational graph, it becomes easier to perform calculations using automatic differentiation and gradient-based optimization techniques.

### Auto-Encoders: An Introduction

Auto-encoders are a type of artificial neural network that are trained to encode and decode data to learn a latent representation of the input. The basic architecture of an auto-encoder consists of an input layer, one or more hidden layers, and an output layer. The input layer takes in the input data while the output layer produces the reconstructed output. The hidden layers in between are responsible for learning the compressed representation of the input data.

Auto-encoders can be used for various tasks such as data compression, feature extraction, and anomaly detection. They are particularly effective when dealing with high-dimensional data such as images and text. By learning a compressed representation of the data, they can eliminate noise and redundancy present in the original dataset.

Overall, auto-encoders are an important tool in the field of machine learning and are widely used in various applications such as image and speech recognition, natural language processing, and data analysis.

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### Exploding and Vanishing Gradients

In the area of machine learning and deep neural networks, the problems of exploding and vanishing gradients are relatively common. Exploding gradients can occur when the gradients of a loss function from each layer of a neural network become excessively large during training, causing numeric overflow, saturation, and instability in the model. In contrast, vanishing gradients can occur when the gradients become too small, causing the model to converge too slowly or not at all. The problems of exploding and vanishing gradients are particularly problematic in deep neural networks with many layers, and there are several techniques available to mitigate these issues, including using specific gradient initialization techniques, selecting appropriate activation functions, and applying regularization methods.

### Understanding the P-Value and its significance in the Null Hypothesis

In statistical hypothesis testing, the p-value is the probability of obtaining test results as extreme as or more extreme than the observed results, assuming that the null hypothesis is correct. In simpler terms, it measures the likelihood of obtaining the observed results if the null hypothesis were true.

The null hypothesis is a statement that assumes there is no significant difference between two groups or variables being tested. The p-value gives an understanding of whether we should reject or accept the null hypothesis.

If the p-value is less than the significance level (commonly set at 0.05), we reject the null hypothesis, which means that the observed results are statistically significant and not simply due to chance. On the other hand, if the p-value is greater than the significance level, we fail to reject the null hypothesis, which means that we cannot conclude that there is a significant difference between the groups being tested.

In conclusion, the p-value is a critical factor in hypothesis testing as it helps us understand whether the results are significant or not and whether we should accept or reject the null hypothesis.

### Why TensorFlow is the Preferred Library for Deep Learning

As someone with experience in the field of deep learning, I can confidently state that TensorFlow is the most preferred library in this area. There are several reasons for this:

**1. Flexibility:** TensorFlow is an open-source library that offers great flexibility to users, allowing them to build and deploy machine learning models across a range of applications, devices, and platforms.

**2. High performance:** TensorFlow is designed to leverage GPUs and other accelerators to deliver high performance, making it ideal for large-scale deep learning projects.

**3. Ease of use:** TensorFlow is easy to use and offers a comprehensive set of tools and resources to help users get started quickly, even if they have no prior experience in machine learning or deep learning.

**4. Active community:** TensorFlow has a large and active community of developers and researchers, who continually contribute to the library's development and improvement.

**5. Integration with other libraries:** TensorFlow can be easily integrated with other popular deep learning libraries, such as Keras and PyTorch, making it even more versatile and powerful.

Overall, TensorFlow is the preferred library for deep learning due to its flexibility, performance, ease of use, active community, and integration capabilities.

### Strategies for Dealing with a Dataset with Missing Values

If a dataset has variables with missing values of over 30%, there are several strategies to deal with it:

1. Delete the variables: If the missing values are spread evenly across all variables, and the variable with missing values is not significant for the analysis, the variable can be deleted.

2. Delete the missing values: If the percentage of missing values is relatively small, the missing values can be deleted. However, if the missing values are not randomly distributed, this approach could introduce bias in the analysis.

3. Impute the missing values: Imputation is the process of replacing missing data with substitute values. There are several methods for imputing missing values, such as mean imputation, median imputation, hot deck imputation etc. However, imputing too many missing values can lead to inaccurate results. So, the imputation method should be selected carefully.

4. Use machine learning algorithms: Machine learning algorithms can be used to predict the missing values based on the available data. For example, a linear regression model can be used to predict missing values based on the relationship between the variable with missing values and other variables.

Ultimately, the strategy chosen will depend on the specific dataset and the needs of the analysis.

### Cross-Validation: Definition and Explanation

Cross-validation is a technique commonly used in machine learning to assess how accurately a predictive model can perform in practice. It involves dividing a dataset into two or more subsets, then training the model on one subset and testing it on another. This process is repeated multiple times, with different subsets used for training and testing each time.

The advantage of cross-validation is that it can help to reduce overfitting, which occurs when a model is too complex and is able to fit the training data too well, but may not generalize well to new data. By evaluating the model on multiple subsets of the data, cross-validation can give a more realistic estimate of how well the model will perform on new, unseen data.

There are several types of cross-validation, including k-fold cross-validation, which involves dividing the data into k equally sized subsets or folds, and leave-one-out cross-validation, which involves using one data point as the testing set and the remaining data as the training set. The choice of cross-validation technique depends on the size and nature of the dataset, as well as the specific problem being addressed.

### Differences between Correlation and Covariance

In statistics, covariance is a measure of the joint variability of two random variables, whereas correlation measures the strength and direction of the linear relationship between two variables. Covariance can take any value between negative infinity and positive infinity, whereas correlation ranges between -1 and 1. Also, covariance is affected by scale, whereas correlation is not. This means that changing the scale of the variables will change the value of covariance, but not the correlation. Lastly, covariance can be used to calculate the variance of a single variable, while correlation cannot.

### Approaching a Data Analytics based Project

When addressing a Data Analytics project, the first step is to understand the problem that needs to be resolved. Once you have a clear understanding of the problem, you can begin collecting the relevant data and evaluating its quality. Then, you can proceed with cleaning, transforming, and analyzing the data as needed. You can use various data analysis tools and techniques to extract insights and identify trends. Finally, you can create a comprehensive report and visualize the results with visual aids such as charts, graphs, or dashboards. Throughout the process, it is important to continuously communicate with stakeholders to ensure that your approach aligns with their expectations and requirements.

```
// Sample code demonstrating loading and cleaning of a CSV file in Python
import pandas as pd
# Load data from CSV
data = pd.read_csv("filename.csv")
# Remove null values
data = data.dropna()
# Clean data as needed
data['date'] = pd.to_datetime(data['date'])
# Analyze data and extract insights
insight_1 = data['column_name'].mean()
# Visualize results
import matplotlib.pyplot as plt
plt.plot(data['column_name'], data['profit'])
plt.title('Profit vs. Column Name')
plt.xlabel('Column Name')
plt.ylabel('Profit')
plt.show()
```

### How often should we update a machine learning algorithm in practice?

In the field of machine learning, the frequency of algorithm updates depends on several factors. One critical factor is the availability of new data. If there is new data that the algorithm has not been trained on, updating the algorithm may be necessary to improve its accuracy.

Another factor is the algorithm's performance. If the algorithm is not achieving the desired results, it may be time to update it. Additionally, changes in the environment, such as new regulations or technological advancements, may require algorithm updates to adapt to new conditions.

Ultimately, the decision to update a machine learning algorithm should be based on a careful evaluation of these factors and should be done with caution to avoid disrupting ongoing operations.

### Importance of Selection Bias

Selection bias is a crucial aspect to consider in research because it can significantly impact the accuracy and validity of the results obtained. Ignoring selection bias can lead to incorrect conclusions based on biased data, thereby making the findings unreliable and misleading. Understanding and addressing selection bias is essential to ensure that research outcomes represent an accurate representation of the population being studied. Therefore, it is necessary to account for selection bias in any research study to obtain credible and trustworthy results.

### Importance of Data Cleaning and Techniques to Clean Data

Data cleaning is crucial because it helps to ensure that data is accurate, consistent, and formatted correctly. Clean data enables more accurate analysis, prevents errors in business decisions, and reduces the risk of data breaches.

Here are some techniques to clean data:

1. Removing duplicates: This involves removing repeated data entries from a dataset, which can skew analysis results.

2. Standardizing data: This involves converting data to a consistent format. For example, converting dates to a standard date format.

3. Handling missing values: Missing values can cause errors in data analysis, so it is important to handle them correctly. This can involve filling in missing values with averages or other statistical measures, or removing incomplete data entries entirely.

4. Removing outliers: Outliers are data points that are significantly different from the rest of the dataset. Removing them can prevent skewing of analysis results.

5. Checking for accuracy: Double-checking data entries for accuracy is important to catch any errors before they can impact analysis or business decisions.

By using these techniques, data can be transformed into accurate, consistent, and reliable information for making informed decisions.

### Available Feature Selection Methods for Building Efficient Predictive Models

There are several feature selection methods available for selecting the appropriate variables for building effective predictive models. Some of these methods include:

1. Filter methods: These methods evaluate the relevance of each feature independently of the others and then choose the relevant features based on some objective criteria, such as correlation coefficient, mutual information, or chi-squared test.

2. Wrapper methods: These methods select subsets of features based on their predictive power. They use a subset of features to train a model and then evaluate its performance on a validation set. Features are added or removed iteratively until the best subset is found.

3. Embedded methods: These methods perform feature selection as an intrinsic part of the model building process. They include techniques such as Lasso, Ridge regression, and decision trees.

4. Dimensionality reduction methods: These methods aim to represent the data in a lower-dimensional space without losing information. Techniques such as principal component analysis (PCA) and linear discriminant analysis (LDA) fall under this category.

Choosing the appropriate feature selection method depends on the nature of the data and the objective of the analysis.

### Dealing with Missing Values during Analysis

As a data analyst, missing values can significantly impact the accuracy of your analysis. Here are some common methods to handle them in your data:

1. Delete the rows with missing values: This is the simplest method but can lead to a loss of a significant amount of data.

2. Mean/Median/Mode Imputation: In this method, we replace the missing values with the mean/median/mode of the available values of that feature.

3. Forward/Backward Fill: In a time-series data, this method replaces the missing values with the previous/next values of that feature.

4. Hot-Deck Imputation: In this method, we replace the missing value with a randomly selected value of the same feature.

5. K-Nearest Neighbors Imputation: In this method, we replace the missing value with the average value of K closest neighboring data points.

The best method to use depends on the type of data, the amount of missing data, and the analysis goals. It is important to carefully evaluate the impact of each method and its potential consequences on the analysis results.

### Will Treating Categorical Variables as Continuous Variables Improve Predictive Modeling?

It is not recommended to treat categorical variables as continuous variables because it can impact the performance of the predictive model. Using the wrong data type can lead to incorrect results or biased model output. It is important to properly encode categorical variables, such as using one-hot encoding, to ensure that they appropriately contribute to the model's predictive capabilities.

### Approach for Handling Missing Values in Data Analysis

When encountering missing values in a data set during analysis, the following approaches can be taken:

1. **Deletion:** Remove all rows or columns that contain missing values. This approach should only be taken when the amount of missing data is insignificant or when there is no other alternative.

2. **Imputation:** Fill in the missing data points with estimated or predicted values. There are several methods for imputing missing values, such as mean imputation, median imputation, and regression imputation.

3. **Analysis:** Analyze the data with missing values as a separate category or perform data analysis by including only the rows or columns that don't have missing values.

The approach taken will largely depend on the amount and nature of the missing data as well as the specific analytical goals.

### Understanding the ROC Curve and its Creation

The ROC curve is a graphical representation of the performance of a binary classifier and its prediction thresholds. It plots the true positive rate (TPR) against the false positive rate (FPR) at various threshold settings. The area under the curve (AUC) is commonly used as a metric to evaluate the trade-off between TPR and FPR.

To create an ROC curve, we first need to obtain the predicted probabilities and true labels for our binary classifier. We then choose various threshold values to convert the probabilistic output into binary predictions. For each threshold, we calculate the TPR and FPR based on the number of true positives, true negatives, false positives, and false negatives. Plotting the TPR versus the FPR for all threshold values creates the ROC curve. The closer the curve is to the top-left corner, the better the classifier's performance.

In summary, the ROC curve is a useful tool to visualize and evaluate the performance of binary classifiers. Creating an ROC curve involves obtaining predicted probabilities and true labels, choosing threshold values, and calculating the TPR and FPR for each threshold.

### Differences between Univariate, Bivariate, and Multivariate Analysis

Univariate analysis involves analyzing a single variable at a time and describing its characteristics such as mean, median, mode, and standard deviation.

Bivariate analysis involves analyzing two variables at the same time to identify the relationships between them. This analysis can be used to determine whether there is a correlation between the variables or to identify factors that contribute to a specific outcome.

Multivariate analysis involves analyzing three or more variables at the same time. It typically involves using advanced statistical techniques to identify relationships between the variables and to determine the relative influence of each variable on the outcome.

Understanding the differences between these types of analysis is critical when conducting research or analyzing data, as they each provide unique insights and can be used to answer different research questions.

```
# Example of Univariate Analysis using Python
import pandas as pd
import matplotlib.pyplot as plt
df = pd.read_csv("data.csv")
df["Age"].describe()
plt.hist(df["Age"])
plt.title("Age Distribution")
plt.xlabel("Age")
plt.ylabel("Frequency")
plt.show()
```

### Understanding Test Set and Validation Set in Machine Learning

In machine learning, the test set is a dataset used to evaluate the performance of a trained machine learning model. The test set should be representative of the real data and should not be used during the training phase to avoid overfitting.

On the other hand, the validation set is used to tune hyperparameters of the model during the training phase. The validation set can be considered as a sample of the training set that is used to validate if the model is learning well during training and to adjust the hyperparameters accordingly.

To summarize, the main difference between the test set and validation set is that the test set is used only for evaluation after the model has been trained, while the validation set is used during training to monitor performance and adjust model parameters. By using both sets correctly, a machine learning model can be trained and evaluated effectively.

### Understanding Kernel Trick

Kernel Trick is a technique used to classify non-linear data by transforming the data into a higher-dimensional feature space. It involves the use of a kernel function to increase the dimensionality of the data, which enables linear algorithms to classify non-linear data. The kernel function forms inner products in the new feature space, resulting in a non-linear decision boundary. This technique is commonly used in Support Vector Machines (SVMs) to classify non-linear data. When using kernel functions, the performance of the classification models can be optimized by selecting a suitable kernel function and the right kernel parameters.

### Differentiating Between Box Plot and Histogram

`A histogram is a chart that displays the distribution of a dataset. It consists of a set of rectangular bars that represent the frequency distribution of the data. The x-axis represents the range of values while the y-axis represents the frequency or number of occurrences. Histograms are mostly used when dealing with large data sets. `

`A box plot is a graphical representation of a statistical distribution that summarizes the median, quartiles, and range of a set of data. The box plot is designed to give a visual representation of the distribution of the data, showing the median, quartiles, outliers, and skewness. It consists of a box and whiskers that extend out from the box. The box represents the middle 50% of the data while the whiskers represent the remaining observations.`

In summary, the key difference between a histogram and a box plot is the way that they summarize the distribution of a dataset. While a histogram provides a graphical display of the frequency distribution, a box plot summarizes data using the median, quartiles, and range. H3. Balancing and Correcting Imbalanced Data in Machine Learning

In machine learning, imbalanced data refers to a situation where the classes in the data are not represented equally. This can lead to biased model performance and inaccurate predictions, particularly for the minority class. Here are some techniques to balance and correct imbalanced data:

1. Oversampling: This involves increasing the number of instances of the minority class in the training data. This can be done through techniques like random oversampling, SMOTE (Synthetic Minority Over-sampling Technique), and ADASYN (Adaptive Synthetic Sampling).

2. Undersampling: This involves reducing the number of instances of the majority class in the training data. This can be done through techniques like random undersampling, Tomek links, and Cluster-based undersampling.

3. Data augmentation: This involves generating new instances for the minority class by applying transformations like rotation, scaling, and flipping.

4. Changing the classification threshold: The default classification threshold of 0.5 can be adjusted to increase the sensitivity of the model towards the minority class.

5. Using different evaluation metrics: Accuracy may not be the best evaluation metric for imbalanced data. Other metrics like precision, recall, F1 score, and AUC-ROC can provide a better understanding of model performance.

It's important to note that the choice of technique depends on the specific problem and data at hand. A combination of techniques may also be necessary for best results.

### What is Better: Random Forest or Multiple Decision Trees?

When it comes to choosing between random forest and multiple decision trees, it depends on the nature of your data and the problem you are trying to solve.

Random forest is generally preferred over multiple decision trees because it helps to reduce the overfitting problem that is common with decision trees. Random forest builds multiple decision trees and then combines them to make a more accurate final prediction. This means that random forest is less likely to make mistakes on new data and is more robust than a single decision tree.

However, if your data is relatively small and simple, and you require a more interpretable model, then multiple decision trees could be the better option. Multiple decision trees are easy to understand and can help you to identify which variables are most important in making a prediction.

In summary, random forest is generally the better option for larger, more complex datasets, while multiple decision trees may be more suitable for smaller, simpler datasets where interpretability is important.

### Probability of Finding Shooting Stars

Assuming that the probability of finding at least one shooting star within a 15-minute interval is 30%, we can calculate the probability of finding at least one shooting star in a one-hour duration using the following formula:

P(X >= 1) = 1 - P(X = 0)

Where:

P(X >= 1) = Probability of finding at least one shooting star in one hour P(X = 0) = Probability of not finding any shooting star in one hour

Since there are four 15-minute intervals within one hour, we can use the binomial distribution formula to calculate the probability of not finding any shooting star in each interval:

P(X = 0) = (0.7)^4

So, the probability of not finding any shooting star in one hour is:

P(X = 0) = (0.7)^4 = 0.2401

Therefore, the probability of finding at least one shooting star in one hour is:

P(X >= 1) = 1 - P(X = 0) = 1 - 0.2401 = 0.7599 or approximately 76%.

### Tossing a Coin from a Jar with One Double-Headed Coin

We have a jar containing 1000 coins, out of which 999 coins are fair and 1 coin is double-headed. We randomly select a coin from the jar and toss it 10 times. We observe 10 heads in a row. We are to estimate the probability of getting a head in the next coin toss.

```
import random
def coin_toss():
"""Simulates a coin toss"""
return random.choice(['H', 'T'])
def experiment():
"""Simulates the experiment"""
coins = ['F'] * 999 + ['DH'] # list containing all the coins in the jar
random.shuffle(coins) # shuffle the coin list
selected_coin = coins[0] # select a random coin
toss_results = [] # list to store the results of the 10 tosses
for i in range(10):
toss_results.append(coin_toss()) # toss the coin and record the result
num_heads = len([result for result in toss_results if result == 'H']) # count the number of heads
if num_heads == 10:
if selected_coin == 'DH':
return 1.0 # if all tosses were heads and the selected coin is double-headed
else:
return 0.5 # if all tosses were heads and the selected coin is fair
else:
return -1.0 # if all tosses were not heads
def estimate_probability(num_experiments):
"""Estimates the probability of getting a head in the next coin toss"""
experiments_results = []
for i in range(num_experiments):
experiments_results.append(experiment()) # record the result of each experiment
num_successful_experiments = len([result for result in experiments_results if result > 0]) # count the successful experiments
probability = float(num_successful_experiments) / float(num_experiments)
return probability
if __name__ == '__main__':
print("Estimated Probability: ", estimate_probability(100000))
```

The code above simulates the experiment of selecting a coin from the jar and tossing it 10 times to observe the number of heads, to estimate the probability of getting a head in the next coin toss. The experiment is repeated a large number of times (in this case, 100000 times) in order to estimate the probability with a higher degree of accuracy.

### Examples where false positive has proven more important than false negative

False positive and false negative are both types of errors in statistical analysis. False positive refers to a situation when an individual is wrongly identified as having a particular condition, while false negative is when an individual who actually has the condition is incorrectly identified as not having it.

There are some scenarios where false positive errors can be more important than false negative errors, for instance:

1. Medical testing: In medical testing, false positives can be more significant than false negatives. Consider a cancer screening test where a false positive is less harmful than a false negative. A false positive would lead to follow-up scans and tests, but a false negative could mean that cancer goes undetected, and treatment is not provided leading to life-threatening consequences.

2. Network security: In the cybersecurity domain, false positives are preferable to false negatives. False positives can raise an alarm that triggers action from the security team, who can further investigate the alert. In contrast, a false negative may fail to detect an actual security breach, leading to data compromise.

3. Drug testing: False positive results in drug testing can have severe consequences for individuals who may lose employment opportunities or face legal penalties, but false negative results can be even more catastrophic as the individual may continue to use drugs which cause harm to their health.

In conclusion, while false positives are not always favorable, there are some scenarios where they are less severe than false negatives. Therefore, careful consideration must be given to the context before entire reliance on a single test result.HIV testing is an example where both false positives and false negatives are equally important. A false positive result means a person is erroneously diagnosed as HIV positive, causing unnecessary stress and medical treatments. A false negative result means a person is erroneously diagnosed as HIV negative, leading to delayed treatment and potential transmission of the virus to others. In both cases, the consequences can be severe, emphasizing the need for accurate HIV testing.

### Should Dimensionality Reduction be Performed before Fitting a Support Vector Model?

When working with a support vector model (SVM), it is generally recommended to perform dimensionality reduction beforehand. This is because SVMs work best when the number of features is relatively small compared to the number of training instances. Therefore, it can be helpful to eliminate irrelevant or redundant features and reduce the number of dimensions in the dataset before fitting the SVM.

Performing dimensionality reduction can also help to reduce overfitting and improve the model's generalization ability. However, it is important to note that the specific method of dimensionality reduction chosen should be based on the characteristics of the dataset and the goals of the analysis.

Overall, while it is not strictly necessary to perform dimensionality reduction before fitting a support vector model, it is often a good idea to do so in order to improve the efficiency and accuracy of the model.

### Assumptions in Linear Regression and their Consequences if Violated

In linear regression, there are several assumptions made regarding the data being analyzed. These assumptions are important to ensure that the model accurately represents the relationships between the variables and that the resulting predictions are reliable. The following are some of the key assumptions:

**Linearity:**The relationship between the independent and dependent variables is linear. If violated, the model may not accurately capture the relationship and the resulting predictions may be inaccurate.**Independence:**The observations are independent of each other. If violated, the model may be biased and the estimated coefficients may not be reliable.**Homoscedasticity:**The variance of the errors is constant across all levels of the independent variables. If violated, the estimated coefficients may still be unbiased, but their standard errors will not be reliable.**Normality:**The errors are normally distributed. If violated, the estimated coefficients may still be reliable, but the standard errors of the estimates will be incorrect.**No or little multicollinearity:**The independent variables should not be highly correlated with each other. If violated, it may lead to unreliable coefficient estimates and difficulty interpreting the model.

Overall, violating these assumptions may lead to biased and inefficient estimates, as well as unreliable predictions. Therefore, it is important to evaluate the assumptions carefully and make appropriate adjustments to the model if necessary.

### Performing Feature Selection using Regularization Method

In order to perform feature selection using regularization method, we can utilize techniques such as LASSO (Least Absolute Shrinkage and Selection Operator) or Ridge Regression. These methods help in selecting a subset of the most important features by shrinking or penalizing the coefficients of the unimportant ones to zero. By doing so, we end up with a model that only includes the significant features, leading to better model interpretation and performance. The strength of the regularization term can be parameterized to control the number of selected features.

### Identifying a Biased Coin

To identify if a coin is biased, one can conduct an experiment by flipping the coin multiple times and recording the outcomes. If the coin is fair and unbiased, the probability of getting either heads or tails is 50%. However, if the coin is biased towards one side, there will be a higher chance of getting that particular outcome.

To ensure accurate results, it is important to repeat the experiment multiple times to rule out any chance occurrences. One can also use statistical analysis to determine the probability of the coin being biased.

### Importance of Dimensionality Reduction

Dimensionality reduction is important in data science and machine learning as it helps to decrease the complexity of the data. High-dimensional data can be quite difficult to interpret and visualize, and can lead to overfitting, increased model complexity, and longer computation times.

By reducing the number of features or dimensions in the dataset, we can reduce noise, improve the accuracy of our models, and speed up the learning algorithm. This helps to eliminate redundant features and irrelevant data, making the model more efficient and effective.

Furthermore, dimensionality reduction can help us to find patterns and relationships in the data that may not be apparent in higher dimensions. This can be especially useful for visualization and exploratory data analysis, as well as for identifying important features and reducing the risk of overfitting.

Overall, dimensionality reduction is an important tool for data scientists and machine learning practitioners, allowing them to work with complex, high-dimensional data more effectively and efficiently. Code:

### Difference between Grid Search and Random Search tuning strategy

When it comes to hyperparameter tuning, two common strategies used are Grid Search and Random Search.

Grid Search involves defining a grid of parameters and evaluating the performance of the model across all possible parameter combinations within the grid. This can be computationally expensive and time-consuming, but it guarantees that the optimal set of parameters will be found within the grid.

On the other hand, Random Search involves randomly selecting combinations of hyperparameters to evaluate the model performance. This approach can be less computationally intensive and may surface good parameter sets earlier than Grid Search. However, there is a chance that the optimal set of parameters may not be found, unlike Grid Search.

In summary, Grid Search is a more exhaustive but reliable method of finding optimal parameters while Random Search provides a simpler and quicker solution with a possibility of not finding the optimal parameters.

### Frequently Asked Questions

62. How should I prepare for a Data Science interview?

```
Preparing for a Data Science interview can seem overwhelming, but here are some tips to help you out:<br>
1. Review and revise basic concepts of Mathematics, Statistics, and Probability.<br>
2. Learn and understand different data structures and algorithms.<br>
3. Practice programming in languages such as Python, R, and SQL.<br>
4. Learn different Data Science libraries such as Pandas, Numpy, and Scikit-Learn.<br>
5. Review and understand Machine Learning models such as Decision Trees, Linear Regression, and Random Forests.<br>
6. Practice solving Data Science problems by using online platforms such as Kaggle.<br>
7. Enhance your communication and presentation skills.<br>
8. Prepare answers to common Data Science interview questions.<br>
Remember, practice makes perfect. Good luck with your interview!
```

### Are Data Science Interviews Difficult?

Data Science interviews can be challenging for many reasons. Firstly, the field itself involves a broad range of topics such as programming, statistics, machine learning, and data visualization, which the interviewer may test a candidate on.

Additionally, companies tend to have various interview formats, including technical coding challenges, case studies, behavioral questions, and presenting past projects. This can make it difficult for candidates to prepare adequately and showcase their skills effectively.

However, thorough preparation and practice can increase a candidate's chances of acing data science interviews. Familiarizing oneself with common data science interview questions, reviewing basic statistics and programming concepts, and practicing code implementations can help one feel more confident during the interview.

```
# Sample code for practicing data science interview questions
# Find the median of a list of numbers
def find_median(numbers):
sorted_numbers = sorted(numbers)
length = len(numbers)
mid_index = length // 2
if length % 2 == 0:
return (sorted_numbers[mid_index - 1] + sorted_numbers[mid_index]) / 2
else:
return sorted_numbers[mid_index]
numbers_list = [4, 2, 7, 1, 9, 3, 8]
median = find_median(numbers_list)
print("The median of the list is:", median)
```

### Top 3 Technical Skills Required for Being a Data Scientist

As a data scientist, having a strong foundation in technical skills is crucial for success. Here are the top three technical skills that are essential for a data scientist:

- Programming Skills: It is imperative for a data scientist to have strong programming skills in languages such as Python, R, SQL, or MATLAB. These programming languages are widely used in the industry and offer a variety of libraries and functions preferable for data analysis.
- Statistics: A data scientist should have a deep understanding of statistical concepts and methods such as hypothesis testing, regression, probability, and Bayesian inference. These statistical techniques enable a data scientist to analyze data, draw insights, and make predictions.
- Machine Learning: Machine learning is at the heart of data science and involves developing algorithms for data analysis, prediction, and decision-making. Some of the popular machine learning methods are decision trees, random forests, support vector machines, neural networks, and deep learning.

Apart from these top three, it is also important for a data scientist to have knowledge of big data technologies like Hadoop, Spark, and Hive, as well as data visualization tools like Tableau, PowerBI, and Matplotlib to communicate their findings with stakeholders.

### Is Data Science a Good Career?

As we move towards a more data-driven world, careers in data science have become increasingly popular. Data science involves analyzing and interpreting complex data sets to gain insights and make informed decisions. So, is data science a good career choice?

The answer is yes, data science can be a very rewarding career. With the demand for skilled data scientists rapidly increasing, the job market in this field is very promising. Data scientists also tend to enjoy high salaries and strong job security.

However, it's important to note that becoming a successful data scientist requires dedication and hard work. A strong foundation in math, statistics, and computer science is essential, as well as an aptitude for problem-solving and creative thinking. Additionally, data scientists must constantly stay up-to-date with the latest technologies and industry trends.

Overall, if you have a passion for working with data and are willing to put in the effort to develop the skills necessary for success, data science can be a very lucrative and fulfilling career choice.

### Are Coding Questions Commonly Asked in Data Science Interviews?

In data science interviews, it is common for interviewers to ask coding questions. These questions can range from simple tasks such as data cleaning and manipulation to more complex challenges such as machine learning algorithms and data modeling. It is important for data science candidates to have a strong understanding of programming languages such as Python or R and to be able to apply that knowledge to real-world scenarios. Having experience with data analysis and visualization tools such as Tableau or Power BI is also often a plus. In addition to coding questions, candidates may also be asked to explain their thought process and problem-solving strategies.

### Is Python and SQL Sufficient for Data Science?

Python and SQL are essential tools for data science, but they may not be enough on their own. Additional skills and knowledge of other tools such as machine learning algorithms, data visualization libraries, and statistics may be required for a successful career in data science. However, Python and SQL form a solid foundation for data science and are widely used in the field. It is important to continually update and expand one's skill set to remain competitive in the rapidly evolving field of data science.

### Understanding Data Science Tools

Data science tools refer to the software and applications that are used by data scientists to analyze and manipulate data, create statistical models, and extract insights from large and complex data sets. These tools are an essential part of the data analysis process and help data scientists to automate repetitive tasks, visualize data, and communicate results effectively. Some commonly used data science tools include programming languages such as Python and R, statistical packages like SAS and SPSS, and data visualization tools like Tableau and Power BI.

### Technical Interview Guides

Here are guides for technical interviews, categorized from introductory to advanced levels.

View All### Best MCQ

As part of their written examination, numerous tech companies necessitate candidates to complete multiple-choice questions (MCQs) assessing their technical aptitude.

View MCQ's