CPI, Probability & Key Terms Explained
A DNA paternity test is a highly accurate scientific method used to determine whether a man is the biological father of a child. While the testing process itself is straightforward, the final report often contains technical terms that can be confusing.
This guide explains how to understand DNA paternity test results in a simple and clear way so you know exactly what your report means.
What Is a DNA Paternity Test Result?
A paternity test result is based on a DNA comparison between a child and an alleged father. The laboratory analyzes specific genetic markers and uses statistical calculations to determine whether a biological relationship exists.
The final report does not usually say simply “yes” or “no.” Instead, it uses scientific terms such as Combined Paternity Index (CPI) and Probability of Paternity.
What Are DNA STR Markers?
DNA is made up of specific regions called Short Tandem Repeats (STRs). These STR markers are highly unique between individuals. Each person inherits:
- One set of STR markers from the mother
- One set from the father
By comparing these markers, scientists can determine whether a biological match exists between the tested individuals.
How Does the DNA Comparison Work?
During testing:
- The child’s DNA is compared with the alleged father’s DNA
- Each STR marker is analyzed
- A match at multiple locations supports paternity
- A mismatch can exclude paternity completely
If the markers do not match, the man is excluded as the biological father. If the markers match across all tested regions, it supports a biological relationship.
What Is the Probability of Paternity?
The Probability of Paternity is shown as a percentage in your report.
- A result of 0% means the man is not the biological father
- A result of 99.9% or higher means he is extremely likely to be the biological father
This percentage reflects how strongly the DNA supports the relationship compared to another random man from the same population.
What Is Combined Paternity Index (CPI)?
The Combined Paternity Index (CPI) is a statistical number that shows how many times more likely it is that the tested man is the biological father compared to a random unrelated man.
For example: A CPI of 500,000 means the tested man is 500,000 times more likely to be the biological father than a random person. A higher CPI means stronger evidence of paternity.
What Do Paternity Test Results Mean?
Your report usually gives one of two conclusions:
1. Not Excluded
This means the tested man is highly likely to be the biological father based on DNA matching.
2. Excluded
This means the tested man is not the biological father, as DNA markers do not match.
Frequently Asked Questions
Conclusion
Understanding DNA paternity test results is essential for correctly interpreting scientific reports and making informed decisions. Key terms such as Combined Paternity Index (CPI), Probability of Paternity, and STR markers explain how genetic comparisons are used to determine biological relationships with a very high level of accuracy.
Whether the result shows inclusion or exclusion, DNA testing provides reliable and evidence-based answers supported by advanced genetic analysis.
For individuals who need dependable testing solutions, accurate DNA paternity testing in Portland offers professional support with confidential handling and scientifically precise results for both personal understanding and legal requirements.