In the procedure for planning sample size, the critical value for t(1−/2;N−p−1) is replaced by the critical z(1−/2) value. Justification for this can be made because precise estimates generally require a relatively large sample size, and replacing the critical t(1−/ 2;N−p−1) value with the critical z(1−/2) value has virtually no impact on the outcome for the sample size in most cases.7 The formula used to determine the planned sample size, such that confidence intervals around a particular population regression coefficient, j, will have an expected value of the width specified, is obtained by solving for N in Equation 1 and by making use of the presumed knowledge of the population multiple correlation coefficients: