You may have DNA match relationship issues and not even know it! Confirmation bias may be affecting your judgment about how you’re related to your DNA matches. You’ll want to know the difference between a genealogical v. genetic relationship, too. Here’s why.
This article was updated in March 2020.
Confirmation bias and DNA matches
One of the biggest problems we have as genealogists, and especially as genetic genealogists, is in confirmation bias.
Confirmation bias: the tendency to process information by looking for, or interpreting, information that is consistent with one’s existing beliefs. -Encyclopedia Britannica
If we see an ancestor in the chart of a DNA match, and we are pretty sure this is also our ancestor, we might be tempted to say that your DNA connection with this match proves that this couple is your shared ancestral couple. But that’s not always the case. You can use the shared DNA to support a connection, given other genealogical information, but DNA can’t ever really prove a connection to anyone outside of your immediate family.
There are several things you can do to avoid confirmation bias when determining your relationships to your DNA matches.
- Check your match’s family tree to see if there are other ancestors you might have in common. (Doesn’t this just seem sensible?)
- Look closely at the genetic relationship possibilities indicated by the amount of shared DNA you have with your matches.
- Compare these possible genetic relationships with your proposed genealogical relationships to make sure they’re consistent, or at least they’re not wildly inconsistent. A genealogical relationship is one that appears on your family tree. It’s documented by family memory and traditional genealogical research. A genetic relationship between two people is circumscribed by the amount of DNA they share.
- Build genetic networks with your DNA matches. More on that below!
There are scenarios in which DNA doesn’t reveal an actual genealogical relationship. Let’s say that Meredith, a documented descendant of your 3x great grandparents Martha and Matthew, had her DNA tested. Your genealogical relationship to Meredith is 4th cousins. However, when the testing company completes the test, Meredith is not found on your match list! Does this mean she really isn’t related to Matthew and Martha? Not necessarily. Even though your genealogical relationship is 4th cousins, your genetic relationship can be non-existent. You will only share DNA with your 4th cousins about 50-60% of the time.
It is also possible to share a certain amount of DNA with someone who isn’t actually your cousin! You will share DNA with individuals who do not share a recent common ancestor with you, but who just share a similar heritage. For example, people from Italy may share DNA with each other not because of a single recent common ancestor, but because of a more distant connection to Italy.
Genetic networks and your DNA matches
Probably the most powerful thing you can do to understand your relationships to your DNA matches is create a series of genetic networks to gather more evidence. This involves using the shared matches tools on your DNA testing website to see who matches both you and your match.
To learn more about working with DNA matches, check out our AncestryDNA Tour. In addition to an overview of working with your matches, you’ll learn about the other features Ancestry offers and how you can make the most of them. The AncestryDNA Tour includes over 90 minutes of video instruction divided into 16 different segments, and comes with a printable, interactive workbook, so you can apply what you learn to your very own tree.
The steps listed in this article constitute part of “reasonably exhaustive research,” which genealogy standards of scholarship say must be accomplished before you can place a DNA match on your family tree with any degree of certainty. Remember, DNA is just another record to use in your journey to document and tell the story of your ancestor, and it can be powerful, if you know how to use it.
An earlier version of this article appeared in December 2018 on genealogygems.com. Rewritten and updated in March 2020 for Your DNA Guide.