Sample Size to Detect a Planned Contrast and a One Degree-of-Freedom Interaction Effect

UNCG Author/Contributor (non-UNCG co-authors, if there are any, appear on document)
Douglas Wahlsten, Visiting Professor (Creator)
Institution
The University of North Carolina at Greensboro (UNCG )
Web Site: http://library.uncg.edu/

Abstract: A simple method is described for estimating the sample size per group required for specified power to detect a linear contrast among J group means. This allows comparison of sample sizes to detect main effects with those needed to detect several realistic kinds of interaction in 2 × 2 and 2 × 2 × 2 designs with a fixed-effects model. For example, when 2 factors are multiplicative, the sample size required to detect the presence of nonadditivity is 7 to 9 times as large as that needed to detect main effects with the same degree of power. In certain other situations, effect sizes for the main effects and interaction may be identical, in which case power and necessary sample sizes to detect the effects will be the same. The method can also be used to find sample size for a complex contrast in a nonfactorial design.

Additional Information

Publication
Psychological Bulletin, 1991, 110, 587-595.
Language: English
Date: 1991
Keywords
Sampling, Pattern recognition, Experiment design, Methodology, Variance