Exercise 24: Describing the Elements of Power Analysis:
Power, Effect Size, Alpha, and Sample Size
Questions to Be Graded
1. 1. When is the optimal time to perform a power analysis—before the beginning of the
study or after the study ends? Provide a rationale for your answer.
The optimal time to perform a power analysis is prior to the study’s beginning so that the
researcher can include an adequate number of participants, because using an inadequate
number of participants puts the study at risk for Type II error.
1. 2. Define effect size.
Effect size: It is a simple way of quantifying the difference between two groups that has
many advantages over the use of tests of statistical significance alone.
1. 3. A researcher is planning to compute a Pearson r. What effect size measure should be
used in the power analysis? Provide a rationale for your answer.
The effect size measure that should be used in the power analysis is the Pearson correlation
coefficient (r) because it serves as its own effect size, as does the odds ratio.
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