Power Tutorial
 Introduction Follow-up Questions Power Calculations

 Pages: E1A  E1B  E1C  E2  QA  E3  QB  E4  QC

## Power Tutorial

Overview: Statistical power is the probability of correctly rejecting a false null hypothesis when a specific alternate hypothesis is true. For example, the ACE training program boasts that their graduates score higher on a standardized test than the population of individuals who do not participate in their training course. Power analysis allows us to determine how likely it is that a test of statistical significance such as a z-test will support the claims of the training program. We also can determine how many cases we need in our sample to attain a specific level of statistical power.

What will I learn? You will learn how statistical power is influenced by four features of the test situation: the size of the difference between the actual population mean and the null hypothesized mean (μ1μ0); variability of scores within groups (s); sample size (N); and alpha error (a). You will use an interactive applet that allows you to manipulate features of the test situation and immediately see the effect on statistical power.

What do I need to know? You should have an understanding of hypothesis testing concepts and procedures. You may want to complete the WISE Hypothesis Testing Tutorial prior to the power tutorial. The examples in this power tutorial are similar to those used in the hypothesis testing tutorial.

What do I need? For this tutorial you will need a paper copy of the WISE Power Lab exercise pages and access to the WISE Power applet. If you do not have a copy of the lab exercise, click here for a printable version of the whole tutorial and or just the worksheet to write down your answers.

Instructions: You will be asked to use the Power applet to simulate sampling data in different situations. You will record data and then interpret your findings in terms of statistical power. Along the way you will be asked questions to test your understanding and you will be given feedback regarding your answers. The end of the tutorial includes some "thought" questions.

Optional review material (one page each):

Begin the Power Tutorial.

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