Quantifying the Problem
Past studies of the postmortem interval show a lack of substantial data.
Investigators often use human substitutes such as pigs or mice. Previous studies have demonstrated that animal models are only of limited use as a proxy for human decomposition.
In the studies that used humans as the study subjects, the sample sizes range from 3-462 individuals. The study with N=462 examined vitreous humor, which is only useful for PMI determinations in a relatively short period around the time of death. The next largest sample size in a review of recent studies examined was 140 individuals. This study examined retrospective case studies from indoor settings. The median sample size among these human studies is 52 and the mean is 86 individuals.
Given the large number of variables known to impact the rate of decomposition, these sample sizes are insufficient for developing accurate models to determine PMI in individual cases. You cannot make a valid conclusion without more substantial data, which is why geoFOR has been created. This application allows you to help fill this critical gap and gather data from vast regions to improve our known samples to develop more reliable methods to determining time since death.
As noted above, information should come from vast areas across the world. This is due to the difference in the environment in each place. These geographically circumscribed areas have a limited range of environment factors that characterize the variables known to impact the rate of decomposition.
The Scientific Working Group for Anthropology (SWGANTH) recognized the key factors of temperature and humidity, burial substrate, burial depth, oxygen content, soil type, soil texture, soil moisture content, soil chemistry, sun exposure, rainfall, insect and scavenger activity, among others. These factors are descriptive of the highly variable conditions that exist in an outdoor context, necessitating multivariate models for estimating PMI that can be applicable to the diverse environmental conditions.
To date, the process of human decomposition has not been modeled over a broad range of environmental conditions across different geographic regions. With the help of geospatial technology geoFOR will be able to add levels of data to each case leading to a better models for estimating PMI.
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Visual example of spatial layers used in GIS models. (https://geog2147.wikispaces.com/Spatial+model)