Screen time and use of social media are related to negative mental health outcomes, including suicidal thoughts (Twenge, Joiner, Rogers, & Martin, 2018). In a national survey of adolescents, the mean number of depressive symptoms was μ = 2.06, σ = 1.00. Suppose that a researcher recruits n = 25 participants and instructs them to visit friends or family instead of using social media. The researcher observes that the average number of depressive symptoms is M = 1.66 after the intervention.

a. Test the hypothesis that the treatment reduced the number of depressive symptoms. Use a one-tailed test with α = .05.

b. If the researcher wants to reduce the likelihood of a Type 1 error, what should they do?

c. Compute Cohen’s d to estimate the size of the effect.

d. Write a sentence demonstrating how the results of the hypothesis test and the measure of effect size would appear in a research report.