Twenty-six girls and 23 boys were recruited from a community-based, after-school program (to be in the treatment group). A control group (n = 41) from a similar after-school program that did not incorporate physical activity programming was added. The control group concentrated mostly on homework completion, reading, and tutoring.

The physical activity protocol (for the treatment group) included 3 days per week of cardiovascular activities in the form of non-competitive tasks and games, which alternated among low, medium, and high intensity over 12 weeks.

Depression and overall negative mood were assessed on the Profile of Mood States-Short Form. Included were scales of Depression (5 items) and Total Mood Disturbance (30 items).

Examine the four means for the "Treatment" group in Table 2, which are reproduced below, along with the difference between Week 1 and Week 12, obtained by subtracting the mean at Week 12 from the mean at Week 1. The values of d are also shown.

1. Notice that the difference between the means is larger for "Total mood disturbance" than for "Depression." Yet the effect size is larger for "Depression" than for "Total mood disturbance." Does this make sense? Explain.

2. Note that the assignment to treatment and control conditions was not done at random. Is this a serious issue? Explain.

3. In light of the sample sizes, how much confidence do you have in the results of this study? Explain.

4.Does the fact that the researcher obtained similar results in two experiments using two very different types of participants increase your confidence in the results? Explain.

treatment group	week 1 mean	week 12 mean	between means	for the difference
depression	4.3	2.4	-1.9	-0.53
total mood disturbance	16.8	11.1	-5.9	-0.35