Internal pilot studies I: type I error rate of the naive t-test

✍ Scribed by Janet Wittes; Oliver Schabenberger; David Zucker; Erica Brittain; Michael Proschan

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 124 KB
• Volume: 18
• Category: Article
• ISSN: 0277-6715
• DOI: 10.1002/(sici)1097-0258(19991230)18:24<3481::aid-sim301>3.0.co;2-c

✦ Synopsis

When sample size is recalculated using unblinded interim data, use of the usual t-test at the end of a study may lead to an elevated type I error rate. This paper describes a numerical quadrature investigation to calculate the true probability of rejection as a function of the time of the recalculation, the magnitude of the detectable treatment e!ect, and the ratio of the guessed to the true variance. We consider both &restricted' designs, those that require "nal sample size at least as large as the originally calculated size, and &unrestricted' designs, those that permit smaller "nal sample sizes than originally calculated. Our results indicate that the bias in the type I error rate is often negligible, especially in restricted designs. Some sets of parameters, however, induce non-trivial bias in the unrestricted design.