A diagnosis of the primary difference between EuroForMix and STRmix

TL;DR

This paper identifies fundamental differences between EuroForMix and STRmix software that cause discrepancies in likelihood ratios, especially for false donors, due to their distinct parameter estimation methods affecting calibration.

Contribution

It provides a diagnostic analysis pinpointing the core cause of likelihood ratio differences between EuroForMix and STRmix, highlighting the impact of parameter estimation procedures.

Findings

Differences in parameter estimation lead to likelihood ratio discrepancies.

EuroForMix shows calibration issues near LR=1 for false donors.

Distinct estimation methods cause the largest LR differences.

Abstract

There is interest in comparing the output, principally the likelihood ratio, from the two probabilistic genotyping software EuroForMix (EFM) and STRmix. Many of these comparison studies are descriptive and make little or no effort to diagnose the cause of difference. There are fundamental differences between EFM and STRmix that are causative of the largest set of likelihood ratio differences. This set of differences is for false donors where there are many instances of LRs just above or below 1 for EFM that give much lower LRs in STRmix. This is caused by the separate estimation of parameters such as allele height variance and mixture proportion under Hp and Ha for EFM. It results in a departure from calibration for EFM in the region of LRs just above and below 1.