Part I: A prediction prior to analysis

Prior to doing the power analysis, examine the group means and standard deviations in the table above. Assume the standard deviation for both groups is 12. Would you expect a large, medium, or small effect when examining the differences between genders on ADDSC? Why?

Part II: Post hoc analysis

1. Compute the effect size (gamma) with gender as the grouping variable and ADDSC as the dependent variable.
2. Compute delta.
3. Compute power using a .05 alpha and a two-tailed test. If you are using G*Power, make sure you have selected the independent t-test and the two-tailed option.
4. Interpret the meaning of the three values you just calculated.

Part III: A priori analysis

1. Assume the effect size that you calculated above in part 1. How many total subjects (N) would be needed to obtain a power of .90?
2. Would you have expected a required N of this size? Why or why not? Interpret the meaning of a .90 power value. Note that G*Power will provide the combined N (the N for both groups).

Part IV: A prediction and analysis

1. Suppose you now wanted to determine whether there was a significant difference between the means for the women versus the men. Reviewing the descriptive information and the calculated power value in Part II, would you expect there to be a significant difference between the means? Why or why not?
2. Using the appropriate statistical procedure, test the between group means for a significant difference. Report the SPSS results and your conclusion.

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