Confidence intervals for prevalence by sample size

Estimating the infection prevalence of a pathogen among collected ticks is something we do often. However, because we are only sampling a portion of the tick population, the number of positive ticks we detect is consistent with a range of possible values of infection prevalence among the entire population, depending on how many ticks were sampled.

This chart is a quick reference for 95% confidence intervals, based on a binomial distribution, of infection prevalence based on a range of sample sizes.