A diagnosis of the primary difference between EuroForMix and STRmix

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.