Power and Precision is a stand-alone program for determining the sample size and statistical power for a planned study. Power and Precision enables you to:

• Find optimal sample size
• Compute statistical power
• Estimate confidence intervals
• Create reports, tables, and graphs

The program is an invaluable resource for market researchers, experimental psychologists, medical researchers, or anyone who is involved in the process of designing studies or preparing grant applications.

Take the Guesswork Out of Power and Precision Analysis
Determining the appropriate sample size and statistical power for a study is essential in planning research. If you choose too small a sample, your study results may prove statistically insignificant. However, if you select too large a sample size, you may create unnecessary work, wasting time and money. Yet few researchers take this initial analysis step because of the complexity of calculating these values.

Created by three leading experts in the field of statistical power analysis -- Dr. Michael Borenstein, Dr. Jacob Cohen, and Dr. Hannah Rothstein -- Power and Precision provides a simple yet highly effective method for analyzing sample size and calculating a statistical test’s power.

With Power and Precision, you can easily compute power and precision (confidence intervals) for many statistical procedures. The program allows you to work interactively and automatically apply Cohen’s effect size conventions for small, medium, and large effects.

Easy-to-Use Features for Learning and Teaching
The program’s intuitive interface makes high-level power and precision analysis easily accessible to students and new users. Many of the procedures are initiated by simple point-and-click interactions. You can generate tables and graphs with one simple click! To aid in the analysis, you can take advantage of the “Wizard” interactive guide and extensive help system.

• Manipulate effect size, alpha, sample size and see immediate impact on power
• Find required sample size automatically (user may specify allocation ratio)
• Take account of power and confidence interval width simultaneously
• Use interactive guide (“Wizard”) to learn program features
• Use continuous summary to understand the meaning of computed data

• One group against a null of zero
• One group against a user-specified null
• Paired/change against a null of zero
• Paired/change against a user-specified null
• Two independent groups, enter difference score
• Two independent groups, enter mean for each group

• One group against a null of 50%
• One group against a user-specified null (Binomial)
• Two independent groups (Power options include Chi-square and Fisher Exact test. Indices include rate difference, relative risk and odds ratio)
• McNemar test of paired proportions
• KxC test of independent proportions (up to 8 rows by 8 columns)
• Sign test

• One group against a null of zero
• One group against a user-specified null
• Two groups

• One-way analysis of variance/covariance
• Two-way fixed effects factorial analysis of variance/covariance
• Three-way fixed effects factorial analysis of variance/covariance

• Includes templates for common designs including covariates followed by main effects; main effects followed by interactions; dummy-coded variables; and polynomial regression
• Allows the user to customize the study design with up to 10 sets of variables and 99 variables per set
• Computes power for the increment of R2 at each step and also for the cumulative R2 at each step
• Allows the user to compute power for sequential groups of sets

• Computes power using the non-central t-distribution; includes assistants for one-sample and two-sample t-tests
• Computes power using the non-central F-distribution; includes assistants for ANOVA and for multiple regression
• Computes power using the non-central chi-square distribution; includes assistants for a KxC test of independence

• Power is available for all procedures
• Confidence intervals are available for t-tests and z-tests, one sample proportions, two independent sample proportions, and one sample correlation
• Tolerance intervals are available for t-tests
• Tools for Computing Power
• Find N required for specified power
• Allows unequal N’s
• Cohen’s effect size conventions
• Store scenarios to list
• List may be scrolled, copied, printed
• Save data to disk

• Power as a function of sample size
• Power as a function of effect size, alpha, and sample size
• Confidence intervals as a function of sample size for mean, mean difference, standard difference, single proportion, difference between proportions, relative risk, log relative risk, odds ratio, log odds ratio, correlation
• Standard error as a function of sample size for mean, mean difference, rate difference, correlation

• Full-page text report for all procedures
• Report includes discussion of both power and confidence interval width
• Reports, tables and graphs may be copied to clipboard and pasted into word-processing program

• Interactive guide
• Interactive Summary
• Tip of the day
• Windows 95® Help system including Table of Contents, Index, Step-by-Step Help and worked examples

• Windows 95® or NT®
• VGA or SVGA monitor
• 12 MB hard disk space

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