A researcher is interested in whether a new antidepressant drug D has an effect on people's self-rating of depression.She randomly assigns 12 people into two groups so that each group has 6 people. One group is given drug D daily, and the other group is not given drug D.Call these the Drug group and the No Drug group, respectively.After one month of treatment, all 12 people were asked to rate on a scale from 1 to 7 how depressed they felt, where 1 = not depressed at all and 7 = very depressed.The following are the data:

drug=2,3,4,4,2,3,[ND=6

[MD=3

[ SD=0.89

no drug 4,5,5,4,6,6[nND=6

MD=3

SD=0.89

Using an ?-level of .05, perform a two-tailed t-test to determine whether there was an effect ofDrug D on depression ratings.Specifically, answer the following questions:

1. What is the total degrees of freedom for this problem?
2. Calculate the standard error of the difference between sample means.
3. Calculate the t-score for the difference between sample means, MD-MND
4. Using Table T, what is the critical value of t for this problem?
5. Based on the relationship between the value of t you calculated in (3) and the critical value of t from (4), can the researcher conclude that there is an effect of Drug D on on depression ratings?

A graduate student realized that the depression study above in Question 4 should have had a placebo condition in which a third group was given a pill just as the people in the Drug condition were, but where the pill was not Drug D (e.g., a sugar pill). So she designed a new experiment with three conditions -- Drug, No Drug, and Placebo. To perform the experiment, the graduate student randomly assigned 18 people into the three groups so that each group has 6 people. After one month of treatment, all 18 people were asked to rate on a scale from 1 to 7 how depressed they felt, where 1 = not depressed at all and 7 = very depressed. The following are the data: Drug No Drug Placebo 2 4 5 3 5 5 4 5 6 4 4 5 2 6 4 3 6 5 r"D = 6 nND = 6 r1p|acebo = 6 MD = 3 MND = 5 Mplacebo = 5 Using an a-Ievel of .05, perform an Analysis of Variance (ANOVA) to determine whether there is a difference among the three conditions. Specifically, answer the following questions: What is the within condition degrees of freedom, dfwimin? What is the within condition sum of squares, SSwithin? What is the within condition mean squares, MSwnhin? What is the between condition degrees of freedom, dfbetween? What is the between condition sum of squares, SSbe'ween? What is the between condition mean squares, MSbe'ween? Calculate the F-value for this experiment. Using Table F, choose the appropriate critical value of F for this problem. Based on the relationship between the value of F you calculated in U) and the critical value of F you chose in (8), can the researcher conclude that there is a difference among the three conditions? SOPNQWPP'NT