t-test in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a one-sample t-test in R

What is the output of this R code snippet?

R Programming

set.seed(123)
x <- rnorm(10, mean=5, sd=2)
t.test.result <- t.test(x, mu=5)
round(t.test.result$p.value, 3)

A 0.564

B 0.045

C 0.123

D 0.001

💡 Hint

Check the p-value from the t.test object and round it to 3 decimals.

The t.test compares the sample mean to mu=5. The p-value is about 0.564 after rounding.

🧠 Conceptual

intermediate

Understanding paired t-test in R

Which option correctly describes what this R code does?

R Programming

before <- c(200, 195, 210, 190, 205)
after <- c(198, 192, 215, 188, 207)
t.test(before, after, paired=TRUE)

A Performs a paired t-test comparing means of before and after measurements on the same subjects.

B Performs an independent two-sample t-test assuming equal variances.

C Performs a one-sample t-test comparing before to zero.

D Performs a paired t-test but ignores pairing and treats data as independent.

💡 Hint

Look at the paired=TRUE argument and the two vectors before and after.

The paired=TRUE argument tells R to do a paired t-test comparing the two related samples.

🔧 Debug

advanced

Identify the error in this two-sample t-test code

What error will this R code produce?

R Programming

group1 <- c(5, 7, 8, 6)
group2 <- c(6, 9, 7)
t.test(group1, group2, paired=TRUE)

A Error: object 'paired' not found

B Error: 'x' and 'y' must have the same length for paired t-test

C No error, runs successfully and returns p-value

D Error: cannot perform t-test on numeric vectors

💡 Hint

Check the lengths of group1 and group2 when paired=TRUE.

Paired t-test requires both vectors to have the same length because it compares pairs element-wise.

❓ Predict Output

advanced

Output of Welch Two Sample t-test in R

What is the output of this R code snippet?

R Programming

set.seed(42)
g1 <- rnorm(15, mean=10, sd=3)
g2 <- rnorm(20, mean=12, sd=5)
test <- t.test(g1, g2)
round(test$statistic, 2)

A -2.30

B 1.45

C -1.45

D 2.30

💡 Hint

Check the t-statistic value from the test object and round to 2 decimals.

The t-statistic is negative because g1 mean is less than g2 mean. The rounded value is about -1.45.

📝 Syntax

expert

Identify the syntax error in this t-test code

Which option contains the syntax error that will cause R to fail running the code?

A t.test(x, mu=5, alternative='two.sided')

B t.test(x, mu=5, alternative='greater')

C t.test(x, mu=5, alternative='less')

D t.test(x, mu=5 alternative='greater')

💡 Hint

Look for missing commas between arguments.

Option D is missing a comma between mu=5 and alternative='greater', causing a syntax error.