An educational psychologist studies the effect of frequent testing on retention

Question

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. Frequent Quizzes Two Exams n = 20 n = 20 M = 73 M = 68 a. 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. [Hint 1: Because the two samples are of same size, the pooled variance is simply the average of the two sample variances. See page 307. Hint 2:If the df is not listed in the table look for the df that is closest to your calculated df. For example if the df=68 you can choose the value for df=60]. b. If the first sample variance is 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 alpha = .05.

Explanation / Answer

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MTB > TwoT 20 73 38 20 68 42;
SUBC>   Pooled.

Two-Sample T-Test and CI

Sample   N Mean StDev SE Mean
1       20 73.0   38.0      8.5
2       20 68.0   42.0      9.4

Difference = mu (1) - mu (2)
Estimate for difference: 5.0
95% CI for difference: (-20.6, 30.6)
T-Test of difference = 0 (vs not =): T-Value = 0.39 P-Value = 0.695 DF = 38
Both use Pooled StDev = 40.0500

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