Forensic entomological evidence is most often used to estimate the postmortem interval (PMI). Satisfactory techniques have not been available to quantify the precision of such a PMI estimate. For Cochliomyia macellaria (F.) (Diptera: Calliphoridae), we describe construction of a confidence interval on age of a larva, given its weight. The method requires a controlled experiment by which weights of larvae are observed at ages spread over sufficient range to cover the time from egg hatch up to postfeeding stage. A statistical model relating distributions of weights to age is formulated and fit to these data. We assumed a simple model in which both means and variances of weight distributions are linearly interpolated between sampled ages. The weight of a larva of unknown age is then compared to the fitted model via inverse prediction to compute the confidence interval on age of the larva.
