How many subjects to screen? A practical procedure for estimating multivariate normal probabilities for correlated variables.
This article suggests a practical procedure for estimating the number of Ss that need to be screened to obtain a sample of fixed size that meets multiple correlated criteria. The procedure is based on the fact that least squares regression provides a good quadratic fit for Monte Carlo estimates of multivariate probabilities when they are plotted as a function of mean pairwise correlations (r) for the criterion variables. The equations given here can be used to predict selected 3- to 5-variable joint probabilities with reasonable accuracy as long as pairwise correlations for the selection criteria range from .10 to .90.
McGraw
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Department of Psychology, University of Mississippi 38677.
Gordji
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Wong
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SP
D006801:Humans; D012106:Research; D012107:Research Design