Peer Review

An Introduction to Statistical Power

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Reviewed:: Sep 26, 2006 by Statistics

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Ratings

Overall Rating:

Content Quality:

Effectiveness:

Ease of Use:

Overview:: This guided exercise employs a Java applet simulation to help users understand statistical power and its relationship to effect size, standard deviation, sample size, and significance level. To gain the full benefits of the exercise, users should understand and be able to perform hypothesis tests. Relevant review materials are available from the links provided. To complete the activity, users will need a copy of the exercise and a computer with an Internet connection and a Java-enabled browser. Users will be asked several questions throughout the activity and will be given feedback regarding their answers. Although detailed solutions are provided, users should try to answer the questions on their own first. The end of the tutorial contains some "thought" questions.
Type of Material:: This activity is a guided exercise that utilizes an Internet Applet.
Recommended Uses:: Designed for individual study, the worksheets can be used in class as a laboratory activity or assigned for homework after an introductory lesson on the concept of statistical power. Upper level undergraduates could use this activity independently as a means of review if they had previous exposure to the topic of statistical power. Teachers could use the applet in a lecture to demonstrate the concept of power.
Technical Requirements:: Students need a computer with an Internet connection and a Java enabled web browser. The students also need either access to a printer or pre-printed versions of the exercise worksheet.
Identify Major Learning Goals:: The user will understand how changes to the effect size, sample size, significance level, or the population standard deviation affect statistical power.
Target Student Population:: This activity is primarily intended for introductory statistics students, though it could be used as a review for advanced students.
Prerequisite Knowledge or Skills:: Students need a solid understanding of the concepts and terminology of hypothesis testing. The web page acknowledges this and directs students to another tutorial for review. Furthermore, students should have seen the definition of power.

Content Quality

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Strengths:: This worksheet is well-written, factually correct, and statistically sound. It covers important issues, such as differences in power and practical significance.
Concerns:: The definition of power is not located on the exercise pages. Initially, the complexity of the applet may be overwhelming for introductory students. For instance, it does not show how power is calculated. Instead, the numerical value of power for a given example is provided based on the values that are typed into the parameter boxes. This is fine if students have already learned what power is. Because students enter parameter values (i.e., sample size, null hypothesis mean) into boxes, they may need help connecting these boxes to real situations. Wording on the worksheet describing the color of the region on the applet associated with the values of the sample mean that lead to rejecting/not rejecting the null hypothesis could be misleading.

Potential Effectiveness as a Teaching Tool

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Strengths:: The well-labeled instructions direct the students¿ focus by having them manipulate one parameter at a time. This methodical process and the visualization provided by the applet help students build intuition and think critically about power, its implications, and how it is affected by certain factors. The graphics, typical of many textbooks, help tie these relationships to the mathematical underpinnings. Summary questions force students to recast their conclusions in a more general context.
Concerns:: Students may be tempted to complete the assignment without thinking about the underlying concepts. In order to receive maximum benefits from using this activity, students need to be highly motivated, independent learners. The user should be aware that time to complete the activity could be a concern depending on the constraints of the given class.

Ease of Use for Both Students and Faculty

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Strengths:: The handouts are consistent with well-written, step-by-step instructions. Assuming students have the necessary equipment, this activity should progress smoothly for the students with very little preparation needed by the teacher.
Concerns:: Faculty might need to spend time explaining the graphics and the interface to students. On first exposure it is a bit overwhelming, since the graphic area has three graphs, two colors, and many different parameter boxes to manipulate. Additionally, some students may have difficulty reading the worksheets and extracting the necessary information.

Other Issues and Comments:: This complete "ready-to-go" lesson is a nice supplemental resource for introducing the basic concepts of statistical power, a concept which is frequently difficult for students. Using this activity in combination with additional practice problems should help students solidify their understanding of these concepts.
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