Equation 2 is intended to determine N such that the expected half-width of an interval is under the researcher’s control. However, there is approximately only a 50% chance that the interval will be no larger than specified. The reason for this can be seen from Equation 1. Notice that the width of an interval will depend in part on R2 and R2XXj, both of which will vary from sample to sample. Thus, for a fixed sample size, the interval width will also vary over replications. However, it is possible to modify Equation 2 in order to increase the likelihood that the obtained interval will be no wider than desired.