Question: Researchers conducted a randomized, double-blind study to measure the effects of the drug olanzapine on patients diagnosed with bipolar disorder. A total of 115 patients with a DSM-IV diagnosis of bipolar disorder were randomly divided into two groups. Group 1 (n₁ = 55) received 20 mg per day of olanzapine, while group 2 (n₂ = 60) received a placebo. The effectiveness of the drug was measured using the Young-Mania rating scale, with the net improvement score recorded. Does the evidence suggest the experimental group experienced a larger mean improvement that the control group at α = .01 level of significance? (4 pts.)

Experimental Group (n₁ = 55): mean improvement 14.8,

standard deviation 12.5

Control Group (n₂ = 60): mean improvement 8.1,

standard deviation 12.7

a. To BEST analyze this data, specifically identify the type of statistical test.

b. What’s the confidence interval?

c. Based on the confidence interval, what’s the research decision?

d. If the researcher decides to fail to reject the null, she’s made

a. The correct decision

i. A Type I error

ii. A Type II error