Why are my DNA test results wrong?


Are you wondering can your DNA results be incorrect? Let me walk you through the answer.


You Don't Need A Test to Know Most of Your DNA


We all have DNA. In fact, 99.9% of our DNA is the same. If you want to go by that, you don't even have to be tested, and you already know what 99.9% of your DNA is.


Should I Believe People Who Claim Their Results are Wrong?


You may have heard some people say, "Oh, I got my DNA tested, but the results are so wrong! It's nothing like what I am."


Or, "Hey, if I get this tested. which company is the most accurate?"


Both of those questions tend to think that your DNA results can be incorrect. But I think most people are asking the wrong question.


Let's look at two ways that our DNA results are correct or incorrect. To listen to Andy explain the two areas where people are concerned about accuracy, watch his video.

Video: Can an DNA tests give you false results?


How Accuracy of Your Raw DNA?


First, the actual raw data of our DNA is made up of three billion letters, A C T's or G's.


In three billion places, we have an A, T, C, or G.


When we're doing a DNA test, commercial genetic genealogy looks at about 500,000 of those places. They have 500,000 chances to get something wrong.


Is something going to go wrong?


Yeah.


Does it happen a lot?


No, not at all. In fact, I've compared my DNA, which's been tested between multiple different companies. Perhaps three of the companies say that I'm an A in this location and A fourth company says I'm a C in this location.


Just by looking at these situations, I have found that less than half a percent of any time that I'm looking at the same location, the DNA testing companies will get it wrong.


Less than half a percent! So that's still 99.5% correct on what they're testing.


Remember, they already know what the other 99.9 is (see above). You're actually looking at a 99.9995% accuracy rating on the raw data judgment calls.


Sometimes a major error happens with the test. Either there's not enough DNA, or something with the sample goes wrong in the processing. When that happens, the company will send you an email and tell you that they had a problem processing your sample. They will invite you to take another test.


Why Are the DNA Testing Companies So Accurate With Raw DNA?


The reason why 23andMe, Ancestry DNA, MyHeritage DNA, Living DNA, and Family Tree DNA can be so accurate is that they're actually running many tests over and over. So they're not just looking at a letter once. They're not just looking at that location once. They're looking at that location several times and analyzing it each time.


If a letter shows up every time in one location, they're confident to say that it is that letter.


If sometimes the analysis says the letter is one thing and a different letter at other times, the companies will determine that location is a "No Call." In other words, they are not going to tell you what that letter is because, for whatever reason, the analysis can't make a consistent decision.


The amount of no-calls that you have in your DNA is also less than that 0.5%. There are just not that many of them.


So, overall, when you get your results that raw data, 99% of it will be the same every single time you test.


If you believe that 99% is not good enough, then yes, you can say that your DNA test is incorrect.


However, I believe that 99% is more than an A. I'm going to say that it is correct


How else can DNA tests be wrong?


The next part of DNA testing is really what people are talking about when they say their results are wrong.


There are three errors where people say their DNA results are wrong:

  • Ethnicity Results

  • DNA Matches

  • Medical Information


Accuracy of Ethnicity Results


With your ethnicity results, one thing to always remember is that the companies will tell you these are ethnicity ESTIMATES. It is not definitive.


The ethnicity estimates indicate where some of your ancestries may have been.


Most of the ethnicity results are great at the continental level and possibly the sub-regional levels.


There are certain populations like Ashkenazi Jews, who have had a separate community from most of the others. So their DNA has remained very separate from the communities around them. And so, the companies can actually pull out what DNA might be Ashkenazi Jewish.


On the other hand, most companies will also drill down to even smaller and smaller levels. One of the problems with this is that there has been much immigration and moving over the last centuries. Just because today's people and maybe the people of an area have lived there for a couple of hundred years doesn't mean that they lived there 300, 400, or 500 years ago.


For that matter, DNA is correct great for ethnicity at the continental level.

But it's really uncertain the smaller down you get.


In some places, when you're talking about a certain county or town, I wouldn't change my birth certificate or change which I think I am based on ethnicity results.


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Accuracy of DNA Matches


There are some definite matches, particularly your close relatives. When the companies find that you match as a brother, father, sister, half-sibling, first cousin, or second cousin, this relationship will appear on the DNA match list of your relatives and your match list.


Now, some people think that companies show the incorrect because some of their first or second cousins don't show up as such on their match list.


When this happens, there likely is something that happened in the family people don't know about or have kept secret.


A father or mother is not the biological father or mother of a close relative.


Now once you get to third and fourth cousins, you don't share DNA with all of them. The further your family relationship, the fewer people you share DNA with, even if you're genealogical kin.


For instance, you share DNA with 90% of your third cousins. This means there are many people that you're related to that you don't share any DNA with.


Additionally, you will find people on your DNA match list that you just can't figure out a connection to. These people usually share 10 - 15 centimorgans with you. There is a percentage of these people that you don't have a genealogical relationship with.


In other words, you're not really related within the last 10 generations. You might be related a thousand years ago, but not in any time that you're going to be able to figure out from a genealogical perspective.


We call such instances false matches.


Now the smaller amount of DNA you share with somebody, the greater the likelihood that they are a false match.


For instance, at around seven centimorgans, 50% of your matches are false matches. You're not going to be able to find any way that you're related.


With three centimorgans in common, more than 90% are false matches.


Compared to 13 or 14 shared centimorgans, about 2% percent of your matches are false matches.


In short, when you're looking at your match data:

  • Close relatives are correct.

  • Distant relatives have a percentage of incorrect or false matches.

You're not going to know which are false from only your test. You actually have to have many different close relative family test to determine whether or not the other relatives is wrong or not.


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Accuracy of Medical DNA Results


The third area then is medical or health information. There are multiple parts to this question.


Certain test results are 100% dependent on our DNA. For instance,

  • hair color

  • eye color

  • blood type

These factors sometimes depend on a single gene or a combination of genes. But these characteristics are dictated by our DNA.


On the other hand, there are many things, like your susceptibility to certain kinds of cancer or the ability to taste different things with a DNA component. But there is no guarantee you'll have the condition.


For instance, just because you have a propensity to obesity or breast cancer doesn't mean that you're a hundred percent going to get it.


Likewise, just because you don't have this propensity or don't have the genes for this also doesn't mean you're not going to get any of these diseases or conditions.


The best that scientists can do is tell you a percentage of how much your genetics affects it. It doesn't tell you whether you're going to have it necessarily.


So again, when we're talking about medical and health information.

  • Some things, yes, whatever your DNA reports are correct.

  • Other things might be incorrect, but it's not because of any processing.


So are your DNA Test Results Wrong?


Before we can tell if our DNA test is correct, we need to understand what aspect of the results we're discussing.


The accuracy depends on what question you are asking.


Learn more about Genetic Genealogy


Continue your study of genetic genealogy through the following posts:



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