Impact Of Various Population Databases

From the three combined STR profile frequencies calculated in Table 21.2 it is apparent that different populations can yield different frequency estimates due to variations in allele frequencies in these populations. A calculation of the same STR profile as used in the previous examples against 97 different published population databases (including the three present in Appendix II) found that the cumulative profile frequency ranged from 1 in 3.43 X 1014 to 1 in 2.65 X1021 (D.N.A. Box 21.1).

The ability to determine simultaneously the frequency for a particular STR profile in multiple population databases was recently made easier with the development of a Microsoft Excel macro called OmniPop. Below the cumulative profile frequency range is calculated for the particular STR profile listed against 166 published population studies involving Profiler Plus kit loci and 97 published reports containing all 13 CODIS core loci. The cumulative profile frequency obtained with U.S. Caucasian alleles present in the Appendix II data set are listed as well.

These profile frequencies were all calculated with a theta value of 0.01. When using a theta value of 0.03 as recommended by NRC II for native (more inbred) populations, the range for the computed profile with all 13 STR loci across the 97 published population data sets is 2.77 x 1014 to 1.27 x 1021.

It is worth noting that the computed profile is part of the U.S. Caucasian data set used to generate the allele frequencies described in Appendix II and thus this database would be expected to compute fairly conservative values for this particular 13-locus STR profile as demonstrated below.

STR Locus

Profile Computed

Number of Populations Used

Cumulative Profile Frequency Range (1 in ...)

Cumulative Profile Frequency against U.S. Caucasians (Appendix II)

D3S1358

16,17

166

5.24 to 62.6

9.19

VWA

17,18

166

37.6 to 1080

81.8

FGA

21,22

166

737 to 119 000

1010

D8S1179

12,14

166

8980 to 5 430 000

16400

D21S11

28,30

166

165 000 to 248 000 000

186 000

D18S51

14,16

166

3.85 x 106 to 2.68x 1010

4.88 x 106

D5S818

12,13

166

2.28x 107 to 4.22 x 1011

4.51 x 107

D13S317

11,14

166

4.32 x 108 to 1.69 x 1013

1.38 x 109

D7S820

9,9

166

1.17 x 1010 to 2.98 x 1016

4.22 x 1010

D16S539

9,11

97

4.06 x 1011 to 1.11 x 1018

5.82 x 10"

TH01

6,6

97

9.30 x 1012 to 1.45 x 1019

1.05 x 1013

TPOX

8,8

97

3.33 x 1013 to 1.54 x 1020

3.63 x 1013

CSF1PO

10,10

97

3.43 x 1014 to 2.65 x 1021

OmniPop 150.4.2 was used for these calculations. This Excel macro is available from Brian Burritt of the San Diego Police Department; telephone: +1 (619) 531 2215; email: [email protected].

STR profile frequency calculations against multiple population databases

Table 21.4

Comparison of statistical treatment for homozygotes and heterozygotes under different assumptions. Allele frequency values (P, Pj) for the TH01 and D13S317 example data are from Appendix II (U.S. Caucasians). Note that if 6 is zero then unconditional and conditional formulas collapse to their Hardy—Weinberg equilibrium (HWE) functions.

It is probably worth noting that the final calculated value in the far right column of D.N.A. Box 21.1 (1 in 7.43 x 1014) differs slightly from that determined in Table 21.2 (1 in 8.37 x 1014) due to the number of significant figures carried throughout the calculations. Thus, in order to obtain consistent frequency estimates with the same allele frequency information it is essential to maintain the same significant figures between calculations.

Another source of population databases that enables an online search is the European Network of Forensic Science Institutes (ENFSI) DNA Working Group STR Population Database located at http://www.str-base.org/ index2.php. An estimated random match probability for a DNA profile of interest can be calculated using allele frequencies produced from 5700 profiles covering 24 European populations that have been generated with the SGM Plus loci (see Chapter 5) (see Gill et al. 2003).

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