Lab Assignment 3
Name: __________________________
Complete all questions and be sure to show all work and calculations. Even if you indicate the correct answer, failure to show all work and calculations will result in missed points for the question. Partial credit can be earned for incorrect responses with appropriate work and calculations demonstrated.
An educational psychologist studies the effect of frequent testing on retention of class material. In one section of an introductory course, students are given quizzes each week. A second section of the same course receives only two tests during the semester. At the end of the semester, both sections receive the same final exam, and the scores are summarized below:
Weekly Quizzes n = 20
M = 73 1.
2.
3.
4.
Two Exams n = 20
M = 68
Write out the null hypothesis and alternative hypothesis for this study.
If the first sample variance is s2 = 38 and the second sample has s2 = 42, do the data indicate that testing frequency has a significant effect on performance? Use a two-tailed test at the .05 level of significance. (Note: because the two samples are the same size, the pooled variance is simply the average of the two sample variances.)
If the first sample variance has s2 = 84 and the second sample has s2 = 96, do the data indicate that testing frequency has a significant effect? Again, use a two-tailed test with α = .05.
Describe how the size of the variance affects the outcome of the hypothesis test.
The following data are from an independent-measures experiment comparing two treatment conditions:
Treatment 1 Treatment 2 6 19
13 9
8 18
4 10
13 12
4 14
11 19
5 11
5. Calculate the mean and standard deviation for Treatment 1 and Treatment 2.
PSY 241: Quantitative Methods in Psychology Lab Assignment 3
Do these data indicate a significant difference between the treatments at the .05 level of significance?
Compute r2 to measure the size of the treatment effect.
Write a sentence demonstrating how the outcome of the hypothesis test and the measure
of effect size would appear in a research report.
