Statistics Quiz

Question 1

What is the difference between covariance and correlation?

Accepted Answer

Correlation is covariance divided by the two standard deviations, so it is unitless and bounded in [-1, 1], while covariance carries the units of both variables and has no fixed scale. That is what makes correlation comparable across pairs; both only capture linear association.

Question 2

What is R-squared?

Accepted Answer

R-squared is a statistical measure of how close the data are to the fitted regression line. It is also known as the coefficient of determination.

Question 3

What is the difference between "long" and "wide" format data?

Accepted Answer

Wide: categorical data is grouped in a single row, long: each row is an observation belonging to a particular category.

Question 4

What is a false positive?

Accepted Answer

An example in which the model mistakenly predicted the positive class.

Question 5

What is dimensionality reduction?

Accepted Answer

It is the process of reducing the number of variables under consideration by obtaining a set of principal variables.

Question 6

What is Survivorship bias?

Accepted Answer

Is the logical error of concentrating on the people or things that made it past some selection process and overlooking those that did not.

Question 7

How can we select K for K-means?

Accepted Answer

Domain knowledge first, then the elbow of inertia against k, average silhouette, or the gap statistic. Inertia falls monotonically, so the elbow is often ambiguous; silhouette scores separation as well as compactness. If a downstream use defines the segments, let that pick k.

Question 8

What is MSE?

Accepted Answer

MSE stands for Mean Squared Error. And is a measure of how close a fitted line is to data points by measuring the average squared of the errors.

Question 9

The normal distribution derives its importance from which famous theorem?

Accepted Answer

The Central Limit Theorem: the sampling distribution of a mean of independent draws approaches a normal as n grows, whatever the population's shape, provided variance is finite. That is what licenses normal-based confidence intervals and t-tests on decidedly non-normal data.

Question 10

In a normal distribution which parameter indicates where the bell is centered?

Accepted Answer

The mean.

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