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Top 30 Data Science Job Interview Questions 2021 – Prepare Yourself to Concrete Your Place

Top 30 Data Science Job Interview Questions 2021 – Prepare Yourself to Concrete Your Place


Data Science has become quite a lucrative field these days. If you are looking for Data Science Job Support, various companies can choose to go for it. Moreover, if you want to work for a reputed Data Science company, you need to first crack a Data Science interview. Here are the top 56 questions to excel in DataScience Job Interview. If you can prepare these questions, then your chance of passing the interview will be higher.

1. What pruning in the Decision Tree is?

If some decision nodes’ sub-nodes are removed, this process is known as opposite splitting or pruning.

2. What is Random Forest? How does it work?

Random Forest is nothing but a machine learning process that performs both classification and regression tasks. This is also utilized for outlier values, dimensionality reduction, etc. This is a kind of ensemble learning process in which several weak models are combined for forming a powerful model.

In this method, multiple trees are grown. Every tree is to give a classification for classifying a new object depending on its attributes. Forest is to select the classification with the most votes. For regression, this is to take an average of the outputs by various trees.

Explain deep learning

3. Explain deep learning

It is a subfield of machine learning inspired by the function and structure of the brain known as an artificial neural network. Various machine learning algorithms are there, such as Neuralnetworks, SVM, Linear regression, etc. Deep learning is an extension of neural networks. Few hidden layers are considered in neural networks, but many hidden layers are considered in deep learning.

4. What differentiates supervised machine learning from unsupervised one?

Supervised machine learning basically needs training labelled data. On the other hand, unsupervised machine learning does not necessarily need any kind of labelled data.

5. How to avoid over-fitting a model?

Over-fitting refers to such a model which is only set for a small amount of data and ignores the bigger picture. 3 effective processes could be used for avoiding over-fitting:

• Keeping this model simple: You should take lesser variables under consideration. It will lessen noise in training data.

• Using cross: Using this validation technique will be helpful. K folds cross-validation is an example of this.

• Using regularization technique: Technique like LASSO can be used to penalize specific model parameters.

6. How Does a ROC Curve Work?

This curve is a graphical representation of the contract between false-positive rates and true positive rates at different thresholds. This is likely to be utilizing a proxy for a trade-off between false positive rate and true positive rate (sensitivity).

7. You have a data set that consists of variables with around 30% missing values. How should you deal with these?

For a large data set, you should just remove rows with the missing data values. This is the fastest way. The rest of the data are to be used for predicting values.

If data sets are small, you can substitute the missing values with the average or mean of the rest of the data utilizing pandas’ data frame in Python. Various ways are to do it like df.fillna (mean), df.mean ().

8. What is an SVM Machine Learning Algorithm?

Support Vector Machine or SVM is nothing but a supervised machine learning algorithm that can perfectly be utilized for Classification and Regression. If your training data set has n features, SVM is to plot this in the n-dimensional space, with every feature being the value of some particular coordinate. This method is to useshyperplanes for separating different classes depending on the kernel function.

9. Explain Dimensionality Reduction Along With its Benefits?

Dimensionality reduction is nothing but a process to convert data set with vast dimensions into the data set with fewer dimensions for conveying similar information concisely.

The reduction is to compress data as well as reduces storage space. This even reduces computation time since fewer dimensions mean less computing. This process is to remove various redundant features. For instance, it is meaningless to store a value in two separate units (inches and meters).

10. How Many Types of Kernel Functions are There in SVM?

4 types of different kernel functions are there in SVM.

1. Sigmoid kernel
2. Radial basis kernel
3. Polynomial kernel
4. Linear kernel

11. What Do You Understand By Recommender Systems?

A recommender system predicts what a user is likely to rate a particular product depending on their choices. This is to be split into two different segments:

Content-based filtering

For instance, Pandora is to use attributes of the song for recommending music with similar attributes. In this regard, you look at the content of the music instead of focussing on who all else is listening to that music.

Collaborative filtering

For instance,  recommends tracks to which other users with similar tastes are to listen. You will also get to see this thing after buying something on Amazon. You as a customer may get a message along with some products: ‘Users that bought it also bought.

Naive Bayes

12. Explain ‘Naive’ in Naive Bayes?

Naive Bayes is nothing but an algorithm that is based on Bayes Theorem. This theorem described the probability of some event as per prior knowledge of the conditions relevant to this event.

This algorithm is known to be ‘Naive’ because this makes some assumptions that might or might not be correct.

13. How to select k for k-means?

The Elbow method is known to be used for selecting k for the k-means clustering. The concept is to run k-means clustering on data set where ‘k’ indicates a number of the clusters.

Within WSS or Sum of Squares, this is defined as the sum of squared distance between every cluster member and its centroid.

14. State differences between regression and the classification ML techniques.

Both of these techniques fall under the supervised machine learning algorithm. Under this algorithm, you need to train the model utilizing a labelled data set. You should explicitly provide correct labels and algorithm tries for learning patterns from the input to output. If the labels are discrete values, this is a classification problem such as A, B etc.But if the labels are continuous values, this is a regression problem such as 1.333, 1.23, etc.,

15. Explain the importance of p-value?

If P-value is ≤0.05, it basically indicates very strong evidence against the null hypothesis. You need to reject this null hypothesis.

In case the p-value is >0.05, it is to indicate weak evidence against the null hypothesis. You should accept this null hypothesis.

If the p-value is at a cut-offof 0.05, it is known to be marginal, which means this could go either way.

16. If your machine has 4GB RAM, you are looking forward to training your model on a 10GB data set. How should you solve this problem?

At first, you need to ask which ML model you need to train.

In the case of neural networks, batch size with the Numpy array is supposed to work.


• Load while data in the Numpy array. This array happens to have attributes for creating a mapping of a complete data set. But this does not necessarily whole data set in the memory.
• You are to pass the index to the Numpy array for getting the needed data.
• Proceed to use the data for passing to the neural network.
• The batch size should be small

In case of SVM, the partial fit is to work well.


• One big data set should be divided into several small data sets.
• You need to use the partial fit process for the SVM. This needs a subset of the complete data set.
• Proceed to repeat step 2 for the other subsets.

17. ‘’People who bought it also bought…’’ recommendation is shown on Amazon after purchasing something. Which algorithm is used in this?

The recommendation engine is to be accomplished with collaborative filtering. This filtering is used to explainthe behavior of the other buyers and their purchase history as per their selection, ratings, etc.

This engine is to make predictions depending on things that may interest a buyer as per the personal choices of the other users. Item features are known to be unknown in this algorithm.

18. You have a dataset on cancer detection. And you built a classification model to achieve an accurate model of around 96%. Should you be happy about it? What could you do about this?

Cancer detection is to result in an imbalanced data set. In this data set, accuracy is not to be based as a measure of the performance. This is crucial to focus on the remaining 4% that represents those patients that were wrongly diagnosed. An early diagnosis is important regarding cancer detection because it can then improve the patient’s prognosis.

Therefore, for evaluating model performance, you are supposed to use true positive rate (sensitivity), true negative rate (specificity), and F measure for determining the class-wise performance of the classifier.

19. Explain TF/IDF vectorization

Term Frequency/Inverse Document Frequency (TF/IDF) is a numerical statistic intended to properly reflect how significant a word is likely to be for a detail in a corpus or collection. This is quite often utilized as a weighing factor in text mining and information retrieval. Value of TF/IDF increases proportionally to several times some word is to appear in the document. But it is offset by the frequency of the word in a corpus that helps in adjusting that few words appear comparatively more frequently.

20. Suppose you want to make the right prediction of death from heart disease on 3 different risk factors like blood cholesterol level, gender, and age. Which algorithm will be most suitable in this regard?

Logistic regression would certainly be the best algorithm to be used in this regard.

21. What is regularization, and explain why this is significant?

This is a process of effectively adding a tuning parameter to some model for inducing smoothness for preventing over-fitting. It is mostly done by properly adding a constant multiple to some existing weight vector. L1 (Lasso0 or the L2 (ridge) is known to be such a constant. This model prediction is to minimize loss function calculated on the regularized training set.

22. On studying the behavior of a population, 4 particular individual types have been identified that will be important for your study. If you want to find the users that are known to be similar to each type, then which algorithm will be most suitable in this regard?

As you are to look forward to group people together, particularly by 4 distinct similarities, this is to indicate the value of k. Hence, K-means clustering will surely be the best option.

23. Explain Selection bias.

This bias is introduced by selecting the group, individuals, or the data for analysis to ensure proper randomization is not achieved. Thus, it ensures the sample obtained is not representative of the population that needs to be analyzed. This is also referred to as the selection effect. Selection bias also refers to the distortion of the statistical analysis. Without this bias, some conclusions of the study may not be correct.

24. Suppose, you have effectively run association rules algorithm on some dataset. Two rules {apple, orange} => {grape} and {banana, apple} => {grape} are found to quite relevant. What other thing is to be true?

The {grape, apple} is going to be another frequent item set that will be relevant.

25. State reinforcement learning

It is such learning about what to do and how to efficiently map situations to actions. It is done for maximizing numerical reward signals. The learner is not normally told which action should be taken, but the learner must discover it. This kind of learning is generally inspired by learning about human beings based on the reward/penalty mechanism.

26. Explain feature vectors

It is such an n-dimensional vector of the numerical attributes that generally represent an object. In machine learning, the feature vectors are utilized to properly represent symbolic or numeric characteristics of some object mathematically.

27. Explain the difference between machine learning and the deep learning

Machine learning is a computer science field which gives computer ability to learn without being programmed explicitly. It can be categorized into 3 segments reinforcement learning, supervised machine learning, and the unsupervised machine learning.

On the other hand, deep learning is a subfield of machine learning that deals with algorithms inspired by the function and structure of the brain, knownsas artificial neural networks.

28. What do you know about root cause analysis?

This analysis was developed for analyzing industrial accidents, but it has other applications now. This problem-solving method is used to isolate the root causes of the problems or faults. Some factor is to be called as the root cause in case its deduction from problem fault-sequence is to avert final undesirable event from happening.

29. What is Normal Distribution?

Data is distributed in various ways with a bias to the right or left, or this can simply be called jumbled up. But there could be chances where data is to be distributed around some central value without any kind of bias to right or left. Hence, it reaches the normal distribution in a bell-shapedcurve. Random variables are distributed in symmetrical bell-shapedcurves.

30. Explain logistic regression

This is also considered to be a logit model. This technique is extensively used for forecasting binary outcomes from the linear combination of the predictor variables.


Working as a data scientist is not easy. But getting a data science job is not an easy task either. If you want to get selected, you must go through all these data science questions-answers to stay ahead of the other aspirants.

It would be an amazing chance for you to stay sharp by studying these questions and answers. These interview questions will be helpful and rewarding for you to say, the least. It will help you move one step closer to your dream job. You have all the good reasons to prepare yourself with these important data science interview questions.

You should thoroughly check out each of the questions and their relevant answers to the best of your ability. This is how you will get to crack your dream data science interview. It will also be beneficial for you in exploring various aspects of data science.

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