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. Test at d=.05. The data are as follows. Testing Frequency Several Two N=21 N = 21 M = 73 M = 68 52 -38 s²= 42 What is the t-value for this test? (Round to two decimal places; Hint: You'll need to back calculate the SS from the variance that's provided for each group)

Answer 1

The test statistic is

$t = \frac{M1 - M2}{\sqrt{\frac{s1^2}{n1} + \frac{s2^2}{n2}}}$

  $= \frac{73 - 68}{\sqrt{\frac{38}{21} + \frac{42}{21}}}$