Document Detail

Sample size determination for a t test given a t value from a previous study: A FORTRAN 77 program.
MedLine Citation:
PMID:  11816459     Owner:  NLM     Status:  MEDLINE    
When uncertain about the magnitude of an effect, researchers commonly substitute in the standard sample-size-determination formula an estimate of effect size derived from a previous experiment. A problem with this approach is that the traditional sample-size-determination formula was not designed to deal with the uncertainty inherent in an effect-size estimate. Consequently, estimate-substitution in the traditional sample-size-determination formula can lead to a substantial loss of power. A method of sample-size determination designed to handle uncertainty in effect-size estimates is described. The procedure uses the t value and sample size from a previous study, which might be a pilot study or a related study in the same area, to establish a distribution of probable effect sizes. The sample size to be employed in the new study is that which supplies an expected power of the desired amount over the distribution of probable effect sizes. A FORTRAN 77 program is presented that permits swift calculation of sample size for a variety of t tests, including independent t tests, related t tests, t tests of correlation coefficients, and t tests of multiple regression b coefficients.
R Gillett
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Behavior research methods, instruments, & computers : a journal of the Psychonomic Society, Inc     Volume:  33     ISSN:  0743-3808     ISO Abbreviation:  Behav Res Methods Instrum Comput     Publication Date:  2001 Nov 
Date Detail:
Created Date:  2002-01-30     Completed Date:  2002-03-18     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  8413015     Medline TA:  Behav Res Methods Instrum Comput     Country:  United States    
Other Details:
Languages:  eng     Pagination:  544-8     Citation Subset:  IM    
School of Psychology, University of Leicester, Leicester LE1 7RH, U.K.
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MeSH Terms
Data Interpretation, Statistical*
Mathematical Computing*
Programming Languages*
Regression Analysis
Sample Size*

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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