Question

A social psychologist records the number of outbursts in a sample of different classrooms at a local school. Based on the statement below, what are the sample size, decision (retain or reject the null hypothesis), and effect size in the study? "The number of outbursts among students at this local school (M = 3) was significantly less than that in the general population, t(39) = 4.19, p < .05 (d = 0.25)." A. Sample size: 39; Decision: Reject the null hypothesis; Effect size: 0.25. B. Sample size: 39; Decision: Retain the null hypothesis; Effect size: 4.19. C. Sample size: 3; Decision: Reject the null hypothesis; Effect size: 0.25. D. Sample size: 3; Decision: Retain the null hypothesis; Effect size: 4.19.

Answer 1

The sample size was 39, the decision was to reject the null hypothesis and the effect size was 0.25.

Option (A) is true.

Step-by-step explanation:

The number of outbursts among students at this local school (M = 3):

This indicates that the mean number of outbursts in the sample of classrooms was 3.

Was significantly less than that in the general population:

This implies that the researchers were comparing the number of outbursts in their sample to a known population mean.

t(39) = 4.19, p < .05:

This indicates that the t-test statistic was 4.19 and the p-value was less than 0.05.

A p-value less than 0.05 is considered statistically significant, meaning that we can reject the null hypothesis.

(d = 0.25):

This indicates that the Cohen's d effect size was 0.25.

Cohen's d is a measure of the effect size, and a value of 0.25 is considered a small effect size.

Therefore,

Option (A) is true.