Understanding Genetic Profiles and Population Statistics for Forensic Analysis, Slides of Statistics

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Popstats Unplugged

th

International

Symposium onHuman Identification

John V. Planz, Ph.D.UNT Health ScienceCenter at Fort Worth

Forensic Statistics

From the ground up…

Transfer evidence^ Laboratory

result

1. Non-match

exclusion

2. Inconclusive-

no decision

3. Match

estimate frequency

Statistical Analysis

Focus on the question being asked…

About “Q” sample

“K” matches “Q” Who else could match “Q" partial profile, mixtures

So, what are we really after?

Quantitative statement that

expresses the rarity of the DNA

profile

Estimate genotype frequency

1. Frequency at each locus

Hardy-Weinberg Equilibrium

2. Frequency across all loci

Linkage Equilibrium

Where Do We Get These Numbers?

1 in 1,000,0001 in 110,000,

POPULATION DATA

and

Statistics

DNA databases are needed for placing

statistical weight on DNA profiles

Because data are not available for every genotype possible, We use allele frequencies instead of genotype frequencies to estimate rarity.

Estimate allele frequencies

by “gene counting”

A

1

n

1

A

2

n

2

A

3

n

3

A

4

n

4

A

k

n

k

n

1

• n

2

• n

3

• n

4

• ... n

k

= 2N

p

1

= n

1

/2N

p

2

= n

2

/2N

p

3

= n

3

/2N

FBI population Data

You can get other population databases

to be used by Popstats if needed