Mathematically optimal decisions in forensic age assessment

Petter Mostad,Fredrik Tamsen,Andreas Schmeling

doi:10.1007/s00414-021-02749-y

Abstract

Forensic age estimation generally involves considerable amounts of uncertainty. Forensic age indicators such as teeth or skeleton images predict age only approximately, and this is likely to remain true even for future forensic age indicators. Thus, forensic age assessment should aim to make the best possible decisions under uncertainty. In this paper, we apply mathematical theory to make statistically optimal decisions to age assessment. Such an application is fairly straightforward assuming there is a standardized procedure for obtaining age indicator information from individuals, assuming we have data from the application of this procedure to a group of persons with known ages, and assuming the starting point for each individual is a probability distribution describing prior knowledge about the persons age. The main problem is then to obtain such a prior. Our analysis indicates that individual priors rather than a common prior for all persons may be necessary. We suggest that caseworkers, based on individual case information, may select a prior from a menu of priors. We show how information may then be collected over time to gradually increase the robustness of the decision procedure. We also show how replacing individual prior distributions for age with individual prior odds for being above an age limit cannot be recommended as a general method. Our theoretical framework is applied to data where the maturity of the distal femur and the third molar is observed using MRI. As part of this analysis we observe a weak positive conditional correlation between maturity of the two body parts.

Highlights

Physiological processes, like the growth of bones and teeth, can usually be described in developmental stages that occur in predictable sequences
In this paper we explore some consequences of applying Bayesian decision theory to age assessment in general
We propose to divide individuals into groups based on why a forensic age assessment is performed for them, and circumstances in their background

Summary

Introduction

Physiological processes, like the growth of bones and teeth, can usually be described in developmental stages that occur in predictable sequences. By studying the prevalence of different stages in subjects of various ages, the stages can be correlated with chronological age. If the studies are large enough and performed on representative populations, such developmental stages can be used as age indicators in Radiological methods are commonly used to observe age indicators, but there is no consensus between different countries on which techniques to use. For example, want to assess whether a person is above or below the age of 18, it is not helpful to use an age indicator that normally is fully developed at that age. You need an age indicator that is still under development at whatever age limit you want to assess, so that you can separate those that are below and above that age, respectively

Methods

Results

Conclusion