Independent-Samples t Test In a cognitive psychology experiment, the researcher is interested in whether encoding condition has a significant effect on memory for a list of words. She recruits subjects to participate in the experiment. Each recruited subject is randomly assigned to either encoding condition A or encoding condition B. The researcher would like to leave the hypothesis non-directional without predicting which encoding condition would lead to better memory, and she sets the significan ce level at a = .05 for a two-tailed test.
Subject ID Encoding A Subject ID Encoding B
1 87 11 85
2 80 12 80
3 78 13 76
4 76 14 77
5 86 15 86
6 77 16 68
7 83 17 85
8 82 18 79
9 91 19 89
10 90 20 85
A. Calculate estimated variance for population 1 (s12) and estimated variance for population 2 (s22).
B. Calculate the pooled variance (Spooled2) from the two population variances (from question a above).
C. Use the pooled variance (from question b above) to calculate the variance for sampling distribution 1 (SM12) and the variance for sampling distribution 2 (SM22).
D. Calculate standard deviation (Stfmegz) of the comparison d istribution.
E. Calculate the t statistic.
F. For the two-tailed test, find the critical t values for this hypothesis test based on the total degree of freedom (from question d above), and the preset alpha level.
G. Compare the calculated t statistic with the critical t value by stating which is more "extreme", and then draw a conclusion about the hypothesis test by stating clearly "reject" or "fail to reject" the null hypothesis.
H. Calculate the pooled standard deviation for the populations (use the pooled variance calculated in question b); and then calculate the standardized effect size of this test.
I. Draw a conclusion based on the hypothesis test result and the effect size. In other words, did encoding condition have a significant effect on memory score? Was the effect small, medium, or large?