Independent samples t-test: Practice #2

A researcher wishes to compare the effectiveness of group therapy to placebo "antidepressants" (i.e., sugar pills that people think are antidepressants) on negative feelings associated with break-ups. He finds 22 people who went through a break-up in the last 2 weeks.

He placeshalf of themin a therapy group that meets every day for 2 weeks. He givesthe other halfthe sugar "antidepressant" (placebo) every day for the same time.

Unfortunately, he soon discovers that two participants from the Group Therapy session are now dating each other. Because he is worried that their data will not be representative of the effects of group therapy,he decides to remove their data from that sample. So now, the Group Therapy sample only includes 9 participants.

The researcher thought that the effects of Group Therapy might be different from those of Placebo antidepressants, but he is not sure how. At the end of the 2 weeks of treatment, he asks all participants to rate their negative feelings on a scale of 1-100 (higher numbers indicate more sadness, grief, depression, etc.).He finds the average negative feelings for the Therapy group is 70 (SD=30) while the Placebo group has an average of 50 (SD=25).

1.Write down your null and research hypothesis.

2.Write down the necessary pieces of information to test your hypotheses.

3.Calculate the test statistic.s²_pooled=t=

4.Find the appropriate critical value(s).

5.Decide what to do with H0

6.Report your final conclusion with the required information.