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An Evaluation of Sampling Methods Used To Produce Insect Growth Models for Postmortem Interval Estimation

NCJ Number
International Journal of Legal Medicine Volume: 129 Issue: 2 Dated: March 2015 Pages: 405-410
Date Published
March 2015
6 pages

This study calculated 95-percent inverse prediction confidence limits for growth curves of the forensically important carrion flies Chrysomya megacephala and Sarconesia chlorogaster (Calliphoridae) at a constant temperature.


Many authors have produced carrion insect development data for predicting the age of an insect from a corpse. Under some circumstances, this age value is a minimum postmortem interval. There are no standard protocols for such experiments, and the literature includes a variety of sampling methods. To the knowledge of the current study's authors, there has been no investigation of how the choice of sampling method can be expected to influence the performance of the resulting predictive model. In the current study, confidence limits constructed on data for entire age cohorts were considered to be the most realistic and were used to judge the effect of various sub-sampling schemes from the literature. Random sub-samples yielded predictive models similar to those of the complete data. Because taking genuinely random sub-samples would require a great deal of effort, the authors considered it worthwhile only if the larval measurement technique was especially slow and/or expensive; however, although some authors claimed to use random samples, their published methods suggest otherwise. Sub-sampling the largest larvae produced a predictive model that performed poorly, with confidence intervals about an estimate of age being unjustifiably narrow and unlikely to contain the true age. The authors believe these results indicate that most forensic insect development studies should involve the measurement of entire age cohorts rather than sub-samples of one or more cohorts. (Publisher abstract modified)

Date Published: March 1, 2015