A SIMPLE METHOD OF SAMPLE-SIZE CALCULATION FOR LINEAR AND LOGISTIC-REGRESSION

A sample size calculation for logistic regression involves complicated formulae. This paper suggests use of sample size formulae for compari ng means or for comparing proportions in order to calculate the requir ed sample size for a simple logistic regression model. One can then ad just the required sample size for a multiple logistic regression model by a variance inflation factor. This method requires no assumption of low response probability in the logistic model as in a previous publi cation. One can similarly calculate the sample size for linear regress ion models. This paper also compares the accuracy of some existing sam ple-size software for logistic regression with computer power simulati ons. An example illustrates the methods. (C) 1998 John Wiley & Sons, L td.