The testing of combined bacteriological samples --- or ``group testing'' --- was introduced to reduce the cost of identifying defective individuals in populations containing small proportions of defectives. It may also be applied to plants, animals or food samples to estimate proportions infected, or to accept or reject populations. Given the proportion defective in the population, the number of positive combined samples is approximately binomial when the population is large: we find the exact distribution when groups include the same number of samples. We derive some properties of this distribution, and consider maximum-likelihood and Bayesian estimation of the number defective.
- Bayesian estimation; bacteriological testing; group testing; hypergeometric distribution; pooled hypergeometric distribution; pooled sample