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The assignment of the number of contributors (N) to a forensic DNA profile is undertaken as part of the interpretation process. There is no requirement for N to be the same for both propositions wi...

Ramos and Gonzalez-Rodriguez introduce the concept of calibration in order to determine whether a system of evidence presentation is a reliable assessor of evidential weight. In this paper, we appl...

The sensitivity and resolution of modern DNA profiling hardware is such that forensic laboratories generate more data than they have resources to analyse. One coping mechanism is to set a threshold, above the minimum required by instrument noise, so that weak peaks are screened out. In binary interpretations of forensic profiles, the impact of this threshold (sometimes called an analytical threshold – AT) was minimal as interpretations were often limited to a clear major component. With the introduction of continuous typing systems, the interpretation of weak minor components of mixed DNA profiles is possible and consequently the consideration of peaks just above or just below the analytical threshold becomes relevant. We investigate here the occurrence of low-level DNA profile information, specifically that which falls below the analytical threshold. We investigate how it can be dealt with and the consequences of each choice in the framework of continuous DNA profile interpretation systems. Where appropr...

Recently, Eric Lander wrote to this journal 1 outlining the view of the President’s Council of Advisors on Science and Technology (PCAST) that empirical testing is required to ensure that the funct...

Weusten and Herbergs1 proposed a simple and intuitive model for predicting the expected height of stutter peaks and the variance about this expectation. Empirical verification of this model is valuable both for the theoretical understanding of the PCR process and for the practical implementation of many interpretation models for DNA mixtures. This paper confirms Weusten and Herbergs’ prediction that the variance of stutter height is inversely proportional to template, with a study of 99 Identifiler profiles.

In this paper, the variability of peak heights for mixed DNA profiles separated on two different models of a capillary electrophoresis instrument is examined. The Applied Biosystems 3500xl instrument produces larger peaks than the 3130xl instrument. If the relative difference in peak heights between the two instruments was a constant factor then all relative heights should be preserved. However, if that factor differed, say, for small versus large peaks then relative heights would change. The effect of peak height and dye on the relative difference in peak height between injections of the same amplicon on a 3500xl and 3130xl instrument for a series of mixed DNA profiles using the Promega PowerPlex 21 multiplex is described. The ratio of peak heights between instrument models resulted in values up to four times higher on the 3500 compared with the 3130. The magnitude of this difference was shown to be dependent on the dye but not on the peak heights themselves. Relative parameters stutter, heterozygote balance, and mixture proportion were very similar between the two instrument models, indicating that the interpretation guidelines developed on one machine are likely to be transportable to different capillary electrophoresis instrument models and different machines of the same model.

This paper investigates the variables that could affect the stutter ratio (SR). Bayesian modelling techniques are used to model the distribution of the SR using the parameters identified: the locus and the longest uninterrupted sequence (LUS). The final model gives an expected estimate for the SR as well as the distribution about this estimate.

The results of empirical testing of forensic DNA probabilities for Australian and New Zealand populations is reported. It is concluded that if consideration is given to relatedness and subpopulation effects, the current model used in most of Australia and New Zealand appears to give very good predictions.