Interpreting Your Paternity Results

Overview

How Your Report Is Structured

Your paternity report is designed to be straightforward. The laboratory tests several specific DNA locations — called Loci — across all tested parties. At each locus, every individual has two numbers: one inherited from their mother and one from their father.

The report compares these numbers between the child and the alleged father. Shared numbers at each locus are used to calculate a Paternity Index (PI) and the final Probability of Paternity.

What Is a Locus?

The word LOCUS (plural: Loci) refers to a specific, known location on the DNA strand. At every locus, each person carries exactly two genetic values — one inherited from their mother and one from their father. The combination of values across all tested loci creates a unique DNA profile.

Example Reports

Inclusion vs. Exclusion Examples

The following tables show how a real paternity report looks for an included and excluded result.

Inclusion Example

Locus	PI	Child	Alleged Father	Mother
D8S1179	8.24	15, 17	15, 18	11, 17
D21S11	4.24	28, 34	32, 34	24, 28
CSF1PO	5.62	11, 12	12, 15	11, 11

The alleged father shares at least one number with the child at every locus (e.g. both carry 15 at D8S1179, 34 at D21S11, 12 at CSF1PO). Each shared number produces a positive Paternity Index (PI). All PI values are multiplied together to calculate the combined Probability of Paternity. Inclusions are reported at ≥ 99.999%. A figure of 99% is the accepted threshold for confirming paternity.

Exclusion Example

Locus	PI	Child	Alleged Father	Mother
D8S1179	0	15, 17	13, 18	11, 17
D21S11	0	28, 34	30, 32	24, 28
CSF1PO	5.62	11, 12	12, 15	11, 11

At D8S1179 and D21S11, the alleged father shares no numbers with the child — the PI at these loci is 0. To reach a formal exclusion, the alleged father must be excluded at a minimum of 3 loci. A PI of 0 at any locus means no paternity contribution could have come from that man. The Probability of Paternity is reported as 0%.

Your Bottom Line

The Two Possible Results

≥99.999%

Inclusion — Paternity Confirmed

The DNA evidence supports biological paternity. Inclusions are reported at a probability of 99.999% or higher; 99% is the accepted threshold for paternity.

0%

Exclusion — Not the Biological Father

The DNA profiles are incompatible at three or more loci. The tested man is excluded as the biological father, and the probability of paternity is reported as 0%.