A researcher had originally intended to select subjects for placement into treatment groups (i.e., the independent variable) based on a median split of their scores on a placement test for the independent variable. However, now he has decided to put in one group only people scoring at least 1 standard deviation above the mean on the placement test and put in the other group only people scoring at least 1 standard deviation below the mean on the placement test. Sample size remains the same.

Directions for this set of practice exercises: A researcher is conducting studies under the following conditions. For each study,

a. State whether the change in condition will tend to increase or decrease the study’s power and

b. If the change in condition affects primarily the numerator or the denominator of the test statistic, state which part is primarily affected.