Question

In a study of the effects of stress on behavior in rats, 75 rats were randomly assigned to either a stressful environment or a control (nonstressful) environment. After 21 days, the change in weight (in grams) was determined for each rat. The table below summarizes data on weight gain.

(The study report gave the standard error of the mean s/√n, abbreviated as SEM, rather than the standard deviation s.)

Group	n	x¯	SEM
Stress	20	23.26	3
No stress	55	29.68	2

What are the standard deviations (±0.001) for the two groups?

A) For "Stress" group s₁ =

B) For "No stress" group s₂ =

C) What degrees of freedom does the conservative Option 2 use for two-sample t procedures for these samples?

Test the null hypothesis of no difference between the two group means against the two-sided alternative for α = 10%.

D) Is the null hypothesis rejected or not rejected?

Answer 1