What Do Paternity Test Results Mean? A Complete Guide
What do paternity test results mean? If you’ve just received your DNA test report, the scientific language and statistics can seem confusing. Terms like “not excluded,” “Combined Paternity Index,” and probability percentages aren’t part of everyday conversation. This guide will help you understand what your paternity test results mean in clear, plain English.
Whether your results show ‘not excluded’ or ‘excluded,’ we’ll explain exactly what each term means, how to read the DNA marker table, and what the statistics tell you about biological relationships.
What is DNA?
DNA contains the instructions that make you who you are, guiding how your body develops and functions. You inherit half your DNA from your mother and half from your father.
The DNA we test at Identilab is highly variable between individuals, meaning it is extremely unlikely that two people will have the same DNA profile (except for identical twins). By comparing DNA profiles, we can assess whether a biological relationship between two or more people is likely.
How Paternity Tests Work: Understanding the Basics
A paternity test determines whether a man is the biological father of a child. A maternity test determines whether a woman is the biological mother of a child.
At Identilab, we analyse 23 DNA markers. Each person tested has two variants (alleles) at each marker, shown as numbers. We compare the child’s alleles to those of the alleged parent to see if the child inherited one from them at every marker.
What Do Paternity Test Results Mean? Two Possible Outcomes
Your paternity test report will show one of two conclusions. Understanding what these mean is essential to interpreting your results correctly. Let’s break down what each of these means in detail.
What Does ‘Not Excluded’ Mean in Paternity Test Results?
If your report says:
ALLEGED PARENT’S NAME is not excluded from identification as the father/mother of CHILD’S NAME
This means the child’s DNA matches the alleged parent’s DNA at every marker tested. In other words, the test confirms biological parentage.
Why don’t we just say “He IS the father”?
Scientific precision requires us to acknowledge we haven’t tested every person on Earth. However, with probability of paternity at 99.9% or higher (often 99.9999999999%), the result is essentially certain.
Understanding the Statistics:
Your “not excluded” result will include two important numbers:
1. Combined Paternity Index (CPI):
- Must be greater than 1,000 to confirm paternity
- Typical results: millions or billions
- Shows how much more likely this man is to be the father compared to a random person
For example:
“Joe Bloggs is 59 million times more likely to produce a child with the required alleles than a random, unrelated man.”
2. Probability of Paternity:
- Must be greater than 99.9%
- Typical results: 99.99% to 99.9999999999%
- Represents statistical certainty
Example:
“This equates to a Relative Chance of Paternity of 99.9999983%.”
What This Means in Practice:
In legal and scientific practice, a probability of paternity of 99.9% or higher is accepted as conclusive evidence that the tested man is the biological father. While not technically 100%, results at this level are regarded as conclusive evidence of a biological relationship.
Reading the DNA Marker Table:
Your report will also include a table showing the DNA markers tested. In this example, the child matches the alleged father at each marker:
| DNA Marker | Child | Alleged Father |
|---|---|---|
| D3S1358 | 16,17 | 14,16 |
| vWA | 15,17 | 14,17 |
| D16S539 | 9,10 | 10,10 |
What Does ‘Excluded’ Mean in Paternity Test Results?
If your report says:
ALLEGED PARENT’S NAME is excluded from identification as the father/mother of CHILD’S NAME
this means the child’s alleles do not match the alleged parent’s at one or more markers, showing they are not the biological parent.
Because a child must inherit half their DNA from their father and half from their mother, mismatches at multiple markers mean exclusion.
| DNA Marker | Child | Alleged Father |
|---|---|---|
| D3S1358 | 16,17 | 14,15 |
| vWA | 15,17 | 14,17 |
| D16S539 | 9,11 | 10,10 |
Here, the child matches the father only at one marker, but this is by coincidence, just like two unrelated people might share traits such as eye colour.
At Identilab, any result that excludes a biological relationship is confirmed by reprocessing the samples twice, ensuring there is no error.
What if My Report Mentions a Mutation?
Sometimes a child and alleged parent will match at every marker except one or two. In these cases, we assess whether this is a true mismatch (meaning the tested person is not the parent) or if it is due to a mutation.
Mutations are natural “genetic typos” that occasionally occur when DNA is passed from parent to child. They’re usually normal, harmless, and have no effect on health. When a mutation is observed, your report will state:
An apparent mutation was observed in CHILD at one genetic marker (GENETIC MARKER – indicated in the results table with an asterisk), resulting in a single mismatch between child and putative parent. An appropriate mutation rate calculation has been performed and incorporated into the combined paternity index.
What This Means:
The mutation is accounted for in the statistical calculations. If the result still shows “not excluded” with 99.9%+ probability, the tested man is considered the biological father despite the apparent mismatch at one marker.
Mutations do not change the validity or accuracy of paternity test results.
Need Help Understanding Your Results?
We understand that DNA test results can sometimes be difficult to interpret. Our scientists are always happy to explain your report clearly and confidentially. If you still have questions regarding your test report, we are always happy to answer them! Please don’t hesitate to call us on +64 3 964 0659 or email us at hello@identilab.co.nz.
