Fcalc®: A Simplified Computer Program for Calculation of Match Probability Estimates in Evaluation of Forensic Casework
Daniel N. Bolon, Janice M.
Williamson, Susan E. Mitchell, and David H. Bing
CBR Laboratories, 800 Huntington Avenue, Boston, MA 02115
× Ø × Ø × Ø × Ø × Ø × Ø × Ø × Ø × Ø × Ø × Ø × Ø × Ø × Ø × Ø
Results obtained from DNA based forensic genetic testing are always quantitatively evaluated based on databases containing allele frequencies found in randomly selected individuals in the general population. Sophisticated population genetics computer programs for the analysis of databases and determining individual genotype and phenotype frequencies are being introduced for national programs such as CODIS. There is still, however, the need to have simple tools that can be used not only to train individuals in the use of populations genetics but that can also be used as a validated method that can be used locally for analysis of forensic DNA test results.
We describe a computer program, Fcalc®, that is designed for Microsoft® Windows 95/NT operating systems to calculate match probability estimates derived from the results of PCR based DNA genetic typing of forensic samples. Fcalc® uses standard Windows controls, including drop down boxes, to allow the user to enter the results of PCR based forensic test results. The program interfaces with database tables of the population allele frequencies, determines phenotype frequency for each individual locus and then calculates a point estimate of combined match probabilities for all the loci analyzed. All test data can be entered on a single screen and the calculations are automatically performed and displayed. The population allele frequencies are entered as a comma-delineated file. The program can use either discreet values or binned data. There are also options for determining significant figures and performing reliability tests of both the data and the frequency tables. Included in the program are calculations based upon recommendations in the 1996 NRC report The Evaluation of Forensic DNA Evidence. This includes the so-called 2p rule, the use of q to account for effects of population substructure and confidence intervals. All data are printed on a single page that can be inserted into a report. The hardware requirements for it are an Intel compatible Pentium computer with 16MB RAM and a hard drive with 5MB of free space.
This program has been designed to carry out a single task: the rapid calculation of combined match probability estimates derived from PCR based systems in a Windows environment and thus essentially eliminates manual calculations. We have found it to be particularly well suited for training laboratory personnel in the fundamental principles used in the quantitative analysis of DNA genetic typing results as well as in performing analysis on forensic case work that is based on PCR technology.
The program will be demonstrated with both genuine as well as mock casework and proficiency test results.
Go to proceedings home page