# Ace Your Data Science Interview: Top Must-Know Statistics Questions

Data science is a field that combines statistical analysis, computer science, and domain expertise to extract insights and knowledge from data. As such, statistics forms the foundation of data science. Statistics is a branch of mathematics that deals with the collection, analysis, interpretation, presentation, and organization of data. In the context of data science, statistics is used to identify patterns, trends, and relationships in data.

Here are the top interview questions and answer on statistics for data scientists

What is statistics?

Statistics is the study of collecting, analyzing, interpreting, and presenting data. It involves applying mathematical and statistical methods to help understand patterns and relationships in data.

What are the different types of data?

There are two main types of data: quantitative and qualitative. Quantitative data is numerical in nature and can be measured, such as height, weight, or age. Qualitative data, on the other hand, is descriptive in nature and cannot be measured in numbers, such as hair color or political affiliation.

What is a population?

A population is the entire group of individuals or objects that you are interested in studying. It can be large or small, depending on the research question and the resources available.

What is a sample?

A sample is a smaller group of individuals or objects selected from the population to be studied. This is often done because it is more feasible to collect data on a smaller group rather than the entire population.

What is the central limit theorem?

The central limit theorem is a statistical principle that states that the sampling distribution of the mean of any random variable will approach a normal distribution as the sample size increases, regardless of the shape of the underlying population distribution.

What is the difference between a parameter and a statistic?

A parameter is a numerical value that describes a characteristic of a population, such as the population mean or standard deviation. A statistic, on the other hand, is a numerical value that describes a characteristic of a sample, such as the sample mean or standard deviation.

What is probability?

Probability is a measure of the likelihood of an event occurring, expressed as a number between 0 and 1.

What is the difference between probability and statistics?

Probability deals with the theoretical study of random events, while statistics deals with the analysis and interpretation of data that has been collected from real-world situations.

What is a probability distribution?

A probability distribution is a mathematical function that describes the likelihood of different outcomes in a random event.

What is the difference between a discrete and continuous distribution?

A discrete distribution describes a probability distribution where the outcomes are countable and have gaps between them, such as the number of heads in a series of coin flips. A continuous distribution, on the other hand, describes a probability distribution where the outcomes are uncountable and have no gaps between them, such as the weight of a person.

What is a normal distribution?

A normal distribution is a continuous probability distribution that is symmetric and bell-shaped. It is often used to model naturally occurring phenomena in which many small random effects are added together.

What is the empirical rule?

The empirical rule is a statistical principle that states that for any normal distribution, approximately 68% of the data falls within one standard deviation of the mean, 95% falls within two standard deviations of the mean, and 99.7% falls within three standard deviations of the mean.

What is the z-score?

A z-score is a measure of how many standard deviations an observation is away from the mean of a distribution. It is calculated by subtracting the mean from the observation and dividing by the standard deviation.

What is the t-distribution?

The t-distribution is a continuous probability distribution that is used when the sample size is small or when the population standard deviation is unknown. It is similar in shape to the normal distribution but has heavier tails.

What is hypothesis testing?

Hypothesis testing is a statistical method used to determine whether a hypothesis about a population is true or not. It involves comparing sample data to what is expected under the null hypothesis, which is a statement that there is no significant difference or relationship between two variables. The results of the hypothesis test provide evidence either for or against the null hypothesis.

What is a null hypothesis?

A null hypothesis is a statement that there is no significant difference or relationship between two variables in a population. In hypothesis testing, the null hypothesis is typically assumed to be true until there is sufficient evidence to reject it in favor of an alternative hypothesis.

What is a p-value?

A p-value is the probability of observing a test statistic as extreme as or more extreme than the one observed, assuming that the null hypothesis is true. It is used in hypothesis testing to determine the statistical significance of the results. A small p-value (usually less than 0.05) indicates that the observed difference or relationship is unlikely to have occurred by chance alone, and the null hypothesis can be rejected.

What is a confidence interval?

A confidence interval is a range of values that is likely to contain the true population parameter with a certain degree of confidence. It is calculated from a sample and provides a measure of the precision of the estimate. The confidence level, which is typically set to 95%, represents the percentage of intervals that would contain the true parameter if the experiment were repeated many times.

What is a type I error?

A type I error occurs when the null hypothesis is rejected even though it is actually true. It represents a false positive result and is sometimes referred to as a “false alarm”. The probability of a type I error is denoted by alpha (Î±) and is usually set to 0.05 or 0.01.

What is a type II error?

A type II error occurs when the null hypothesis is not rejected even though it is actually false. It represents a false negative result and is sometimes referred to as a “miss”. The probability of a type II error is denoted by beta (Î²) and depends on factors such as the sample size, the effect size, and the level of significance.

What is the power of a test?

The power of a test is the probability of correctly rejecting the null hypothesis when it is actually false. It represents the ability of the test to detect a significant difference or relationship between two variables. A high power (usually greater than 0.80) is desirable, as it reduces the likelihood of a type II error.

What is a one-sample t-test?

A one-sample t-test is a statistical test used to determine whether the mean of a sample is significantly different from a known or hypothesized value. It is appropriate when the population variance is unknown or the sample size is small.

What is a two-sample t-test?

A two-sample t-test is a statistical test used to determine whether the means of two independent samples are significantly different from each other. It assumes that the populations have equal variances and are normally distributed.

What is ANOVA?

ANOVA (analysis of variance) is a statistical method used to compare the means of two or more groups. It tests the null hypothesis that there is no significant difference between the means of the groups. ANOVA can be used to test for main effects, interactions, and higher-order effects.

What is a chi-squared test?

A chi-squared test is a statistical test used to determine whether there is a significant association between two categorical variables. It compares the observed frequencies to the expected frequencies under the null hypothesis of independence.

What is the coefficient of determination?

The coefficient of determination, denoted as R-squared, is a statistical measure that represents the proportion of the variance in the dependent variable that is explained by the independent variables in a regression model. It takes values between 0 and 1, where 0 indicates that the model explains none of the variability, and 1 indicates that the model explains all the variability.

What is the difference between correlation and regression?

Correlation and regression are both statistical methods used to measure the relationship between variables. However, correlation measures the strength and direction of the linear relationship between two variables, whereas regression is a method used to model the relationship between a dependent variable and one or more independent variables. Regression is used to predict the value of the dependent variable based on the values of the independent variables.

What is multicollinearity?

Multicollinearity refers to the situation in which two or more independent variables in a regression model are highly correlated with each other. This can cause problems in the regression analysis, as it makes it difficult to determine the effect of each independent variable on the dependent variable.

What is a random variable?

A random variable is a variable that takes on different values with some probability. It is used to model the uncertainty in a system and can take on either discrete or continuous values.

What is the expected value of a random variable?

The expected value of a random variable is a measure of its central tendency. It represents the average value of the variable, weighted by the probabilities of each value occurring.

What is the variance of a random variable?

The variance of a random variable is a measure of its spread. It represents the average of the squared differences between each value of the variable and its expected value, weighted by the probabilities of each value occurring.

What is the covariance between two random variables?

The covariance between two random variables is a measure of the extent to which they vary together. It represents the average of the product of the deviations of each variable from their expected values, weighted by the probabilities of each combination of values occurring.

What is the correlation between two random variables?

The correlation between two random variables is a measure of the strength and direction of the linear relationship between them. It takes values between -1 and 1, where -1 indicates a perfect negative relationship, 0 indicates no relationship, and 1 indicates a perfect positive relationship.

What is a confidence interval for a mean?

A confidence interval for a mean is a range of values within which we can be reasonably certain that the true population mean lies. It is based on a sample mean and the standard error of the mean, and is calculated using a specific level of confidence (usually 95% or 99%).

What is a confidence interval for a proportion?

A confidence interval for a proportion is a range of values within which we can be reasonably certain that the true population proportion lies. It is based on a sample proportion and the standard error of the proportion, and is calculated using a specific level of confidence (usually 95% or 99%).

What is the difference between parametric and nonparametric statistics?

Parametric statistics assume that the data follows a specific distribution, such as the normal distribution, and make inferences about the population based on the parameters of that distribution. Nonparametric statistics make fewer assumptions about the distribution of the data and are based on rankings or other orderings of the data.

What is a Bayesian approach to statistics?

A Bayesian approach to statistics is a framework that uses Bayes’ theorem to update the probability of a hypothesis based on new evidence. It involves specifying a prior probability distribution over the parameters

What is the difference between correlation and regression?

Correlation and regression are two statistical techniques used to explore the relationship between two variables. Correlation measures the strength and direction of the linear relationship between two variables, while regression is used to model the relationship between two or more variables and to make predictions based on the data.

What is multicollinearity?

Multicollinearity is a phenomenon that occurs when two or more independent variables in a regression model are highly correlated with each other. This can cause problems in the model, such as unstable or unreliable estimates of the regression coefficients.

What is the correlation between two random variables?

The correlation between two random variables measures the strength and direction of their linear relationship. It is a standardized measure of covariance, calculated as the covariance divided by the product of the standard deviations of the two variables.

What is a confidence interval for a mean?

A confidence interval for a mean is a range of values within which the true population mean is expected to fall with a certain degree of confidence, based on a sample of data. It is calculated as the sample mean plus or minus a margin of error, which is determined by the sample size and variability.

What is a confidence interval for a proportion?

A confidence interval for a proportion is a range of values within which the true population proportion is expected to fall with a certain degree of confidence, based on a sample of data. It is calculated as the sample proportion plus or minus a margin of error, which is determined by the sample size and variability.

What is the difference between parametric and nonparametric statistics?

Parametric statistics assume that the data follows a specific probability distribution, such as the normal distribution, and use model-based methods to make inferences about the population parameters. Nonparametric statistics, on the other hand, make fewer assumptions about the distribution of the data and use distribution-free methods to make inferences about the population parameters.

What is maximum likelihood estimation?

Maximum likelihood estimation is a method for estimating the parameters of a probability distribution that best explain the observed data. It involves finding the values of the parameters that maximize the likelihood function, which is a function that measures the likelihood of observing the data given the parameters of the distribution. Maximum likelihood estimation is commonly used in parametric statistics.

What is a likelihood function?

A likelihood function is a function that measures the likelihood of observing the data given the parameters of a probability distribution. It is commonly used in maximum likelihood estimation and Bayesian statistics to find the parameters of the distribution that best explain the observed data.

What is the bootstrap method?

The bootstrap method is a resampling technique that involves repeatedly sampling the data with replacement and using these samples to estimate properties of the population, such as the mean or variance. It is useful when the underlying distribution of the data is unknown or when the sample size is small.

What is cross-validation?

Cross-validation is a technique for evaluating the performance of a predictive model by partitioning the data into a training set and a testing set. The model is trained on the training set and then tested on the testing set to measure its accuracy. Cross-validation can help prevent overfitting and improve the generalizability of the model.

What is overfitting?

Overfitting is a phenomenon in machine learning and statistics where a model fits the training data too well and as a result, performs poorly on new or unseen data. Overfitting occurs when a model is too complex and captures noise or random fluctuations in the data, rather than the underlying patterns or relationships.

What is underfitting?

Underfitting is a phenomenon in machine learning and statistics where a model is too simple and fails to capture the underlying patterns or relationships in the data. Underfitting occurs when a model is not complex enough to explain the variation in the data and as a result, performs poorly on both the training and testing data.

What is regularization?

Regularization is a technique used to prevent overfitting in machine learning and statistics by adding a penalty term to the loss function that the model is trying to minimize. The penalty term discourages the model from fitting the training data too closely and encourages it to generalize better to new or unseen data.

What is the L1 norm?

The L1 norm, also known as the Manhattan norm or the taxicab norm, is a measure of distance between two points in a vector space that is equal to the sum of the absolute differences between the corresponding elements of the vectors. It is often used in regularization to promote sparsity in the coefficients of a model.

What is the L2 norm?

The L2 norm, also known as the Euclidean norm, is a measure of distance between two points in a vector space that is equal to the square root of the sum of the squared