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What is the Combined Paternity Index?

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Paternity Index
Paternity index is a likelihood ratio between the chances that the alleged father may pass the paternal gene, compared to the chance that a random man may pass the paternal gene to the child. If the paternity index is zero, it is because the father does not have any matching alleles with the child at that particular marker. If the paternity index is greater than zero it means the father does have a matching allele with the child.

Combined Paternity Index (CPI)
The combined paternity index is the product of all of the individual paternity index values multiplied together and is a measure of the strength of the genetic evidence. The CPI can range from 0 to infinity. When the combined paternity index is 0, it means the alleged father is not the dad. When the combined paternity index is greater than 100 it means the alleged father is the dad, however it cannot be stated simply as “you are the father”. Because the probability of paternity can never be 100% (you will often `see 99.999%), you cannot say “you are the father” because that implies 100% certainty. Therefore, the results are reported as “the alleged father can not be excluded as the biological father of the child”. When the combined paternity index is greater than 0, but less than 100, the results are inconclusive. Inconclusive results are most often the cause of doing a paternity test without the mother. In most instances, inclusion of the mother’s genetic profile into the statistical calculations results in a conclusive result.

Interpretation of Results
We routinely report testing results with a probability of paternity of 99.99% or higher on inclusions and 0.00% on exclusions. If the alleged father and child do not share all of the required markers, then the alleged father is not the father of the child. This is called an "EXCLUSION" and the probability of paternity will be 0.00%. If the child and alleged father share the required markers, then the alleged father cannot be excluded as the biological father and a probability of paternity will be calculated. The minimum probability of paternity in an inclusion will be 99.99% or greater. A DNA paternity report can never provide a 100% probability of paternity because that would require comparing the DNA of the tested man to every other man on this earth, and that is not possible.
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You will find a Combined Paternity Index in your DNA test report stated near the Probability of paternity. After DNA genetic testing is performed, each tested location that matches the other tested party is assigned a frequency, and the combined frequencies from all the genetic matches leads to a "combined paternity index" (CPI), such as 2,346,242. This means that the chance of another random individual matching your DNA pattern is 1 in 2,346,242. We can then use that calculation to arrive at a probability of paternity of 99.999957% (in this example). more
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The Paternity Index will be present in your results and is a number that represents the likelihood of paternity. The number is calculated based on how common the genetic information found in your test result is within your race population. The Paternity Indices for each genetic locus tested are used to calculate a Combined Paternity Index which can result in a 99.999% Probability of Paternity, or even higher in the case of a true match. As an example, if the CPI is 9,999,987 it means the odds of the tested father being the unique biological father are 9,999,987 to one.
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The Paternity Index will be present in your results and is a number that represents the likelihood of paternity. The number is calculated based on how common the genetic information found in your test result is within your race population. The Paternity Indices for each genetic locus tested are used to calculate a Combined Paternity Index which can result in a 99.999% Probability of Paternity, or even higher in the case of a true match. As an example, if the CPI is 9,999,987 it means the odds of the tested father being the unique biological father are 9,999,987 to one.
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The Paternity Index is a number that represents the likelihood of Paternity. The number is calculated based on how common the genetic information found in your test result is within your race population. The Paternity Indices for each genetic locus tested are used to calculate a Combined Paternity Index which can result in a 99.999% Probability of Paternity, or even higher in the case of a true match. As an example, if the CPI is 9,999,987 it means the odds of the tested father being the unique biological father are 9,999,987 to one. more
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The Combined Paternity Index (CPI) is obtained from the individual Paternity Indices obtained for each locus analysed. The CPI is calculated on the basis of the commonality between the genetic information obtained from the analysis against the general population, thereby generating the likelihood of paternity with a maximum result of 99.99999% Probability of Paternity. In our DNA paternity test results both the Probability of Paternity and CPI are quoted. more
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The Combined Paternity Index (CPI) is calculated from the Paternity Indices generated from each individual locus and gives an indication of the likelihood of Paternity between the alleged father and child as compared to analysis with the general population. The result of the CPI can go as high as 99.9999%+ but will never be quoted as 100% for scientific correctness. As you can see in the attached sample reports, both the CPI and Probability of Paternity are shown in the results of our DNA Paternity tests.In the sample result, you an also see that the DNA test report will show on the left hand coloumn each of the 16 loci analsyed. Every person carries 2 copies of a chromosome, one which he inherits from the biological father and the other from the mother. For each loci, 2 numbers are shown (or one in the case where the alleles are identical (homozygous)) representing the size of the allele. These numbers are then used to compare between the persons involved in the testing to see ... more
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