Accuracy in parameter estimation (AIPE) is an approach to sample size planning concerned with obtaining narrow confidence intervals. The standard AIPE approach yields the necessary sample size so that the expected width of a confidence interval will be sufficiently narrow. Because confidence interval width is a random variable based on data, the actual confidence interval will almost certainly differ from (e.g., be larger or smaller than) the expected confidence interval width. A modified AIPE approach allows sample size to be planned so that there will be some desired degree of assurance that the observed confidence interval will be sufficiently narrow. The standard AIPE approach addresses questions such as what size sample is necessary so that the expected width of the 95% confidence interval width will ...