R Programming Language Certification Statistical Analysis & Modeling in R 3

Question 1

What does AIC stand for and what is it used for in R model selection?

Accepted Answer

Akaike Information Criterion; compares model fit while penalizing for complexity

Answer

AIC (Akaike Information Criterion) balances model fit and complexity; lower AIC indicates a better model when comparing alternatives.

Question 2

Which R function computes the variance of a numeric vector?

Accepted Answer

var()

Answer

var() computes the sample variance of a numeric vector using n-1 in the denominator (Bessel's correction).

Question 3

What is the default method used by cor() in R for computing correlation?

Accepted Answer

Pearson

Answer

cor() uses Pearson's product-moment correlation by default; specify method='spearman' or method='kendall' for rank correlations.

Question 4

Which function in R is used to perform a Wilcoxon rank-sum test (non-parametric alternative to t-test)?

Accepted Answer

wilcox.test()

Answer

wilcox.test() performs the Wilcoxon rank-sum (Mann-Whitney) test or Wilcoxon signed-rank test for non-normal data.

Question 5

In R, what does the residuals() function return for a linear model?

Accepted Answer

The difference between observed and fitted values

Answer

residuals() extracts the residuals (observed minus fitted values) from a fitted model object.

R Programming Language Certification Practice Test