Many forensic genetics problems can be handled using structured systems of discrete variables, for which Bayesian networks offer an appealing practical modeling framework, and allow inferences to be computed by probability propagation methods. However, when standard assumptions are violated—for example, when allele frequencies are unknown, there is identity by descent or the population is heterogeneous—dependence is generated among founding genes, that makes exact calculation of conditional probabilities by propagation methods less straightforward. Here we illustrate different methodologies for assessing sensitivity to assumptions about founders in forensic genetics problems. These include constrained steepest descent, linear fractional programming and representing dependence by structure. We illustrate these methods on several forensic genetics examples involving criminal identification, simple and complex disputed paternity and DNA mixtures.
References
Ayres, K. L. and Balding, D. (2005). Paternity index calculations when some individuals share common ancestry., Forensic Science International 151 101–103.
Ayres, K. L. and Overall, A. D. J. (1999). Allowing for within-subpopulation inbreeding in forensic match probabilities., Forensic Science International 103 207–216.
Bajalinov, E. B. (2003)., Linear-fractional Programming: Theory, Methods, Applications and Software. Kluwer Academic, Dordrechts, the Netherlands.
Balding, D. J. and Nichols, R. A. (1994). DNA profile match probability calculation: How to allow for population stratification, relatedness, database selection and single bands., Forensic Science International 64 125–140.
Balding, D. J. and Nichols, R. A. (1995). A method for quantifying differentiation between populations at multi-allelic loci and its implications for investigating identity and paternity., Genetica 96 3–12.
Blackwell, D. and MacQueen, J. B. (1973). Ferguson distributions via Pólya urn schemes., Ann. Statist. 1 353–355.
Butler, J. M. (2005)., Forensic DNA Typing. Elsevier, USA.
Butler, J. M., Schoske, R., Vallone, P. M., Redman, J. W. and Kline, M. C. (2003). Allele frequencies for 15 autosomal STR loci on U.S. Caucasian, African American and Hispanic populations., Journal of Forensic Sciences 48 (4). Available at http://www.astm.org.
Charnes, A. and Cooper, W. W. (1962). Programming with linear fractional functionals., Naval Research Logistics Quarterly 9 181–186.
Mathematical Reviews (MathSciNet):
MR152370
Cotterman, C. W. (1974). A calculus for statistical genetics. Ph.D. Thesis, 1940 Ohio State University. In, Genetics and Social Structure (P. A. Balanoff ed.). Academic Press, New York.
Cowell, R. G., Dawid, A. P., Lauritzen, S. L. and Spiegelhalter, D. J. (1999)., Probabilistic Networks and Expert Systems. Springer, New York.
Cowell, R. G., Lauritzen, S. L. and Mortera, J. (2007a). A gamma model for DNA mixture analyses., Bayesian Analysis 2 333–348.
Cowell, R. G., Lauritzen, S. L. and Mortera, J. (2007b). Identification and separation of DNA mixtures using peak area information using peak area information., Forensic Science International 166 28–34.
Dawid, A. P. and Mortera, J. (1996). Coherent analysis of forensic identification evidence., J. Roy. Statist. Soc. Ser. B. 58 425–443.
Dawid, A. P., Mortera, J., Pascali, V. L. and van Boxel, D. W. (2002). Probabilistic expert systems for forensic inference from genetic markers., Scand. J. Statist. 29 577–595.
Dawid, A. P., Mortera, J. and Vicard, P. (2007). Object-oriented Bayesian networks for complex forensic DNA profiling problems., Forensic Science International 169 195–205.
Egeland, T., Mostad, P. F., Mevåg, B. and Stenersen, M. (2000). Beyond traditional paternity and identification cases: Selecting the most probable pedigree., Forensic Science International 110 47–59.
Ferguson, T. S. (1973). A Bayesian analysis of some nonparametric problems., Ann. Statist. 1 209–230.
Mathematical Reviews (MathSciNet):
MR350949
Fung, W. K. and Hu, Y. Q. (2004). Interpreting DNA mixtures with related contributors in subdivided populations., Scand. J. Statist. 31 115–130.
Gass, S. I. (1969)., Linear Programming: Methods and Applications. McGraw-Hill, New York.
Mathematical Reviews (MathSciNet):
MR266606
Green, P. J. and Richardson, S. (2001). Modelling heterogeneity with and without the Dirichlet process., Scand. J. Statist. 28 355–375.
Jensen, F. V. (1966)., An Introduction to Bayesian Networks. UCL Press and Springer, London.
Laurie, C. and Weir, B. S. (2003). Dependency effects in multi-locus match probabilities., Theoretical Population Biology 63 207–209.
Lauritzen, S. L. (2003). Some modern applications of graphical models. In, Highly Structured Stochastic Systems (P. J. Green, N. L. Hjort and S. Richardson, eds.). Oxford Statistical Science Series 27 13–32. Oxford Univ. Press, Oxford.
Lauritzen, S. L. and Spiegelhalter, D. J. (1988). Local computations with probabilities on graphical structures and their application to expert systems (with discussion)., J. Roy. Statist. Soc. Ser. B. 50 157–224.
Mathematical Reviews (MathSciNet):
MR964177
Mortera, J., Dawid, A. P. and Lauritzen, S. L. (2003). Probabilistic expert systems for DNA mixture profiling., Theoretical Population Biology 63 191–205.
Mortera, J. and Vicard, P. (2008). Discussion of “Statistical analysis of an archeological find.”, Ann. Appl. Statist. 2 91–96.
R Development Core Team (2005)., R: A Language and Environment for Statistical Computing. R Foundation for Statistical Computing, Vienna, Austria.
Rannala, B. (1996). The sampling theory of neutral alleles in an island population of fluctuating size., Theoretical Population Biology 50 91–104.
Song, Y. S. and Slatkin, M. (2007). A graphical approach to multi-locus match probability computation: Revisiting the product rule., Theoretical Population Biology 72 96–110.
Thompson, E. A. (1974). Gene identities and multiple relationships., Biometrics 30 677–680.
Vajda, S. (1975)., Problems in Linear and Nonlinear Programming. Griffin, London.
Weir, B. (2007a). The rarity of DNA profiles., Ann. Appl. Statist. 1 358–370.
Weir, B. S. (2007b). Matching and partially matching DNA profiles., Journal of Forensic Sciences 49 1009–1014.
Wright, S. (1940). Breeding structure of populations in relation to speciation., American Naturalist 74 232–248.
Wright, S. (1951). The genetical structure of populations., Annals of Eugenics 15 323–54.
Mathematical Reviews (MathSciNet):
MR41413