Modified exact sample size for a binomial proportion with special emphasis on diagnostic test parameter estimation.

The design of epidemiologic studies for the validation of diagnostic tests necessitates accurate sample size calculations to allow for the estimation of diagnostic sensitivity and specificity within a specified level of precision and with the desired level of confidence. Confidence intervals based on the normal approximation to the binomial do not achieve the specified coverage when the proportion is close to 1. A sample size algorithm based on the exact mid-P method of confidence interval estimation was developed to address the limitations of normal approximation methods. This algorithm resulted in sample sizes that achieved the appropriate confidence interval width even in situations when normal approximation methods performed poorly. Copyright 2005 John Wiley & Sons, Ltd.