ENFSI DNA WG STR Population Database Formulae

To calculate match probabilities, the questioned sample is first combined with the European database to make a sample size n+1, in every population assessed. This corrects for sample bias and prevents zero frequencies being recorded for rare alleles that have not been observed in the current database collection. The methods and validation is described by Gill et al (2003) Forensic Science International 131, 184-196 [5].

The formulae used are as follows:

Actual matching probability

		heterozygotes
		homocygotes

Balding & Nichols (1994)

		heterozygotes
		homocygotes

Confidence Intervals (NRC-Report 1996)

		heterozygotes
		homocygotes
	then...

Balding (1995) size bias correction

		heterozygotes
		homocygotes