Question

Researchers using the Roland-Morris Disability Questionnaire as its tool for collecting disability data want to compare two treatment groups. They believe that a 2.5 group difference would be important to them. The literature implies that the common standard deviation for the groups for this questionnaire is 3.7 points.

a. What sample size do they need to detect this difference at 80% power, with a level of significance of .05 using a two-tailed independent test?

b. How would you adjust these sample sizes if you expect a 15% drop out rate.

Answer 1

a)

b)

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