R Programming Language Certification Research & Evidence-Based Practice 3

Question 1

Which R function performs a Shapiro-Wilk test to assess whether a variable follows a normal distribution?

Accepted Answer

shapiro.test()

Answer

shapiro.test() implements the Shapiro-Wilk normality test, returning a W statistic and p-value.

Question 2

In evidence-based research with R, what does a p-value below 0.05 conventionally indicate?

Accepted Answer

The result is statistically significant at the 5% level

Answer

A p-value < 0.05 means there is less than a 5% probability of observing the data if the null hypothesis were true.

Question 3

Which R function computes Cohen's d for measuring effect size between two groups?

Accepted Answer

cohens_d() from the effectsize package

Answer

The effectsize package provides cohens_d() to calculate Cohen's d standardized mean difference.

Question 4

A researcher fits a logistic regression in R using `glm(y ~ x, family = binomial)`. What does the model predict?

Accepted Answer

The log-odds of y being 1

Answer

Logistic regression with binomial family models the log-odds (logit) of the binary outcome.

Question 5

In R, `cor.test(x, y, method = 'spearman')` is preferred over Pearson correlation when:

Accepted Answer

Data are ordinal or the relationship is monotonic but not linear

Answer

Spearman correlation is a rank-based non-parametric method appropriate for ordinal data or non-linear monotonic relationships.

R Programming Language Certification Practice Test