# Mean Difference for the Main Effect of Treatments

18. For the data in the following matrix:

No treatment Treatment

Male M=5 M=3 Overall M =4

Female M=9 M=13 Overall M= 11

Overall M = 7 Overall M=8

a. Describe the mean difference that is the main effect for the treatment.

b. Describe the mean difference that is the main effect for gender.

c. Is there an interaction between gender and treatment? Explain your answer. Looking at the information above, does it appear that the treatment results depend on gender? Why?

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#### Solution Preview

Ch 14, #18. For the data in the following matrix:

No treatment Treatment

Male M=5 M=3 Overall M =4

Female M=9 M=13 Overall M= 11

Overall M = 7 Overall M=8

a. Describe the mean difference that is the main effect for the treatment.

When we're looking at main effects, we're considering each variable in its entirety, or collapsed over the levels of the other variable. In this question, we have two independent variables (IVs), treatment and gender. Each of those IVs has two levels (treatment/no treatment and male/female). To discuss the main effect of the treatment IV, we want to look at the mean score for each level of it, while ignoring the male and female differences on each level of treatment. That is, we want to compare the overall mean of 7 (no treatment) to ...

#### Solution Summary

The mean differences for the main effects of treatments are examined.