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ABSTRACT
Due to the increased sensitivity of genotyping kits developed in recent years, laboratories were able to recover more usable information from smaller amounts of DNA on items of evidence (e.g., touch evidence). This led to increased submission of touch or trace DNA items, which in turn increased the overall workload (van Oorschot, Ballantyne, and Mitchell Citation2010).
In this work, the data collected from approximately 650 cases and 2,000 evidence items was analyzed in order to study the work efficiency, to optimize evidence items processing and to give guidelines for reducing the workload. We examined three aspects: the DNA profiling efficiency for each item type; the number of samples required to obtain a DNA profile from an item; the number of items needed to be examined to obtain a database eligible profile for each case.
To examine DNA profiling efficiency of various items, the productivity Index (PI) grade was calculated on a scale of 0–10 which measures the success rate and the amount of work required for DNA profiling. To the best of our knowledge, this is the first study that measures the combination of DNA profiling success rate and the work required to obtain it.
Body fluids items (blood and saliva) were the most efficient biological sources for DNA profiling (PI 6) while clothing items were less efficient (PI 2.6). Touch items were the least efficient (PI 1.6).
The successful recovery rate of a single source or a major DNA profile increased when items were sampled twice rather than once. No significant increase was obtained when items were sampled more than twice.
Four to five items per case was found to be the optimal number of items to be tested in a case in order to reduce the workload and increase the number of DNA profiles included in the DNA database.