## Statistics Interview Questions & Answers

1. Question 1. What Is Bayesian?

Bayesians condition on the data actually observed and consider the probability distribution on the hypotheses.

2. Question 2. What Is Frequentist?

Frequentists condition on a hypothesis of choice and consider the probability distribution on the data, whether observed or not.

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4. Question 3. What Is Likelihood?

The probability of some observed outcomes given a set of parameter values is regarded as the likelihood of the set of parameter values given the observed outcomes.

5. Question 4. What Is P-value?

In statistical significance testing, the p-value is the probability of obtaining a test statistic at least as extreme as the one that was actually observed, assuming that the null hypothesis is true. If the p-value is less than 0.05 or 0.01, corresponding respectively to a 5% or 1% chance of rejecting the null hypothesis when it is true.

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7. Question 5. Give An Example Of P-value?

Suppose that the experimental results show the coin turning up heads 14 times out of 20 total flips

• null hypothesis (H0): fair coin;
• observation O: 14 heads out of 20 flips; and
• p-value of observation O given H0 = Prob(≥ 14 heads or ≥ 14 tails) = 0.115.

The calculated p-value exceeds 0.05, so the observation is consistent with the null hypothesis – that the observed result of 14 heads out of 20 flips can be ascribed to chance alone – as it falls within the range of what would happen 95% of the time were this in fact the case. In our example, we fail to reject the null hypothesis at the 5% level. Although the coin did not fall evenly, the deviation from expected outcome is small enough to be reported as being “not statistically significant at the 5% level”.

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9. Question 6. What Is Sampling?

Sampling is that part of statistical practice concerned with the selection of an unbiased or random subset of individual observations within a population of individuals intended to yield some knowledge about the population of concern.

10. Question 7. What Are Sampling Methods?

There are four sampling methods:

• Simple Random (purely random),
• Systematic( every kth member of population),
• Cluster (population divided into groups or clusters)
• Stratified (divided by exclusive groups or strata, sample from each group) samplings.
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12. Question 8. What Is Mode?

The mode of a data sample is the element that occurs most often in the collection.

x=[1 2 3 3 3 4 4]

mode(x) % return 3, happen most.

13. Question 9. What Is Median?

Median is described as the numeric value separating the higher half of a sample, a population, or a probability distribution, from the lower half. The median of a finite list of numbers can be found by arranging all the observations from lowest value to highest value and picking the middle one

median(x) % return 3.

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15. Question 10. What Is Quartile?

• second quartile (50th percentile) .
• third quartile (75th percentile) .
• kth percentile.
• prctile(x, 25) % 25th percentile, return 2.25.
• prctile(x, 50) % 50th percentile, return 3, i.e. median.
16. Question 11. What Is Skewness?

Skewness is a measure of the asymmetry of the data around the sample mean. If skewness is negative, the data are spread out more to the left of the mean than to the right. If skewness is positive, the data are spread out more to the right.

Skewness(x) % return-0.5954

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18. Question 12. What Is Variance?

variance describes how far values lie from the mean.

var(x) %return 1.1429

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20. Question 13. What Is Kurtosis?

Kurtosis is a measure of how outlier-prone a distribution is.

kurtosis(x) % return2.3594

21. Question 14. What Is Moment?

Quantitative measure of the shape of a set of points.

moment(x, 2); %return second moment

22. Question 15. What Is Covariance?

Measure of how much two variables change together.

y2=[1 3 4 5 6 7 8]

cov(x,y2) %return 2*2 matrix, diagonal represents variance.

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24. Question 16. What Is One Sample T-test?

T-test is any statistical hypothesis test in which the test statistic follows a Student’s t distribution if the null hypothesis is supported.

[h,p,ci] = ttest(y2,0)% return 1 0.0018 ci =2.6280 7.0863

25. Question 17. What Is Alternative Hypothesis?

The Alternative hypothesis (denoted by H1 ) is the statement that must be true if the null hypothesis is false.

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27. Question 18. What Is Significance Level?

The probability of rejecting the null hypothesis when it is called the significance level α , and very common choices are α = 0.05 and α = 0.01.

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29. Question 19. Give Example Of Central Limit Theorem?

Given that the population of men has normally distributed weights, with a mean of 173 lb and a standard deviation of 30 lb, find the probability that

a. if 1 man is randomly selected, his weight is greater than 180 lb.

b. if 36 different men are randomly selected, their mean weight is greater that 180 lb.

Solution: a) z = (x – μ)/ σ = (180-173)/30 = 0.23

For normal distribution P(Z>0.23) = 0.4090

b) σ x̄ = σ/√n = 20/√ 36 = 5

z= (180-173)/5 = 1.40

P(Z>1.4) = 0.0808

30. Question 20. What Is Binomial Probability Formula?

P(x)= p x q n-x n!/[(n-x)!x!]

where n = number of trials.

x = number of successes among n trials.

p = probability of success in any one trial.

q = 1 -p.

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32. Question 21. Do You Know What Is Binary Search?

For binary search, the array should be arranged in ascending or descending order. In each step, the algorithm compares the search key value with the key value of the middle element of the array. If the keys match, then a matching element has been found and its index, or position, is returned. Otherwise, if the search key is less than the middle element’s key, then the algorithm repeats its action on the sub-array to the left of the middle element or, if the search key is greater, on the sub-array to the right.

33. Question 22. Explain Hash Table?

A hash table is a data structure used to implement an associative array, a structure that can map keys to values. A hash table uses a hash function to compute an index into an array of buckets or slots, from which the correct value can be found.

34. Question 23. Explain Central Limit Theorem?

As the sample size increases, the sampling distribution of sample means approaches a normal distribution.

If all possible random samples of size n are selected from a population with mean μ and standard deviation σ, the mean of the sample means is denoted by μ x̄ , so,

μ x̄ = μ

the standard deviation of the sample means is:

σ x̄ = σ⁄√ n

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36. Question 24. What Is Null Hypothesis?

The null hypothesis (denote by H0 ) is a statement about the value of  a population parameter (such as mean), and it must contain the condition of equality and must be written with the symbol =, ≤, or ≤.

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38. Question 25. What Is Linear Regression?

Modeling the relationship between a scalar variable y and one or more variables denoted X. In linear regression, models of the unknown parameters are estimated from the data using linear functions.

polyfit( x,y2,1) %return 2.1667 -1.3333, i.e 2.1667x-1.3333

39. Question 26. When You Are Creating A Statistical Model How Do You Prevent Over-fitting?

Over-fitting can be prevented by cross-validation.

40. Question 27. What Is Descriptive Statistics?

We study in descriptive statistics the methods for organizing, displaying, and describing data.

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42. Question 28. What Is A Sample?

When data are collected in a statistical study for only a portion or subset of all elements of interest we are using a Sample.

43. Question 29. Give An Example Of Inferential Statistics?