Question

Psych 241 – Quantitative Methods in Psychology Lab Assignment #3

Name:__________________________________

Complete all questions and be sure to show all work and calculations. Partial credit can be earned for incorrect responses with appropriate work and calculations demonstrated. Conversely, points will be reduced if you have the right answer but do not show your work. Good luck!

A clinical psychologist wants to determine if the number of support group sessions a therapy patient attends has an effect depression. The psychologist randomly assigns one group of 6 patients to attend support groups once a month. Another group of 6 patients attends support group sessions once a week. At the end of 6 months, every patient is asked to rate their depression severity on a scale from 1-10 (10 being most depressed). The results are summarized below.

(Hint: For help, follow steps on pages 278 – 279 in your textbook)

Monthly Support Groups n=6
M = 6.34

Weekly Support Groups n=6
M = 2.67

1. Write out the null hypothesis and the alternative hypothesis for this independent measures/between-subjects study both in statistical terms and in English.

2. Find the degrees of freedom and the critical region, using a two-tailed .05 alpha level.

3. Calculate the pooled variance for the two samples if the first sample variance is s2 = 3.47 and the second

   sample variance is s2 = .67. (Note that these two samples have equal sample sizes, so the pooled variance

   will simply be the average of the two sample variances.)

4. Calculate the estimated standard error.

5. Compute the t-statistic. Does if fall in the critical region?

6. Do the data indicate that frequency of support group attendance had a significant effect on depression

   scores? Write out your conclusion as you would in a report.

7. Let’s say that, instead, the first sample variance is s2 = 12.03 and the second sample variance is s2 = 5.23,

   does the data indicate that frequency of support group attendance had as significant effect on self-reported

   depression severity? Use a two-tailed test at the .05 significance level.

8. Describe how the variance affects the outcome of the hypothesis test.

The following is a data set from an independent-measures study comparing two different therapy approaches:

Therapy 1 Therapy 2 5 12
6 11 25

8 13 99 12 5 5 10 5 11

9. Calculate the mean and standard deviation for Therapy 1 and Therapy 2.

10. Do these data suggest that there is a difference between these two therapies at the .05 significance level (two-tailed)? (Do an independent samples t-test)

11. Calculate r2 to measure the size of the treatment effect.

12. Write a sentence that describes the outcome of this study as you might right it up in an actual research

    report.

Answer 1