Sample Size Calculations for Surveys to Substantiate Freedom of Populations from Infectious Agents
Article first published online: 11 MAR 2004
Volume 60, Issue 1, pages 165–171, March 2004
How to Cite
Johnson, W. O., Su, C.-L., Gardner, I. A. and Christensen, R. (2004), Sample Size Calculations for Surveys to Substantiate Freedom of Populations from Infectious Agents. Biometrics, 60: 165–171. doi: 10.1111/j.0006-341X.2004.00143.x
- Issue published online: 11 MAR 2004
- Article first published online: 11 MAR 2004
- Received June 2002. Revised July 2003. Accepted September 2003.
- Gibbs sampling;
- Hypergeometric distribution;
- Risk analysis;
Summary. We develop a Bayesian approach to sample size computations for surveys designed to provide evidence of freedom from a disease or from an infectious agent. A population is considered “disease-free” when the prevalence or probability of disease is less than some threshold value. Prior distributions are specified for diagnostic test sensitivity and specificity and we test the null hypothesis that the prevalence is below the threshold. Sample size computations are developed using hypergeometric sampling for finite populations and binomial sampling for infinite populations. A normal approximation is also developed. Our procedures are compared with the frequentist methods of Cameron and Baldock (1998a, Preventive Veterinary Medicine34, 1–17.) using an example of foot-and-mouth disease. User-friendly programs for sample size calculation and analysis of survey data are available at http://www.epi.ucdavis.edu/diagnostictests/.