The effect of varying the number of contributors in the prosecution and alternate propositions.pdf (796.3 kB)

The effect of varying the number of contributors in the prosecution and alternate propositions (Accepted Manuscript)

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journal contribution
posted on 01.05.2020, 00:05 by John S. Buckleton, Jo-Anne Bright, Kevin Cheng, Hannah Kelly, Duncan Taylor
Using a simplified model, we examine the effect of varying the number of contributors in the prosecution and alternate propositions for a number of simulated examples.

We compare the Slooten and Caliebe [1] solution, with several existing practices. Our own experience is that most laboratories, and ourselves, assign the number of contributors, N = n, by allele count and a manual examination of peak heights. The LRn for one or a very few values is calculated and typically one of these is presented, usually the most conservative. This gives an acceptable approximation.

Reassessing the number of contributors if LR = 0 and adding one to N under both Hp and Ha to “fit” the POI may lead to a substantial overstatement of the LR.

A more reasonable option is to allow optimisation of the assignment under Hp and Ha separately.

We show that an additional contributor explained the single locus profile better when This is pleasingly in line with current interpretation approaches.

Collectively these trials, and the solid theoretical development, suggest that implementation of the Slooten and Caliebe approach is optimal.

Funding

US National Institute of Justice: Grant No. 2017-DN-BX-K541

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