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Arden Miller, Ph.D

Professor of Psychology
Missouri State University


Psychological Statistical Methods




Unit 7: Decision Errors, Power, and Effect Sizes

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Objectives and Lecture Notes
Reading: Aron, Chapter 6

1. Explain the two types of decision errors that occur when conducting hypothesis tests.

2. Compute an effect size and explain how it is useful in putting statistical significance in context and in conducting metaanalysis.

3. Given an effect size, N, and population parameters, compute the power that goes with a statistical test.

4. Demonstrate an understanding of how variance, effect size, and sample size work together to influence the power of a statistical test and discuss statistical and methodological alternatives for increasing the power of statistical test.

5. Discuss the comparative roles of effect size and statistical significance in evaluating the meaning of a study.


Power computation
QA Power & Effect size