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  • TIP Report

    I'm having a problem understanding a report.

    I have two second cousins. One did the y67 and the other the y111. Their ancestry has been documented for over a hundred years. I am also a second cousin, female. We've all been documented through atDNA as 2nd cousins. There seems to not be any doubt. We, also, all match many, many others from the same surname atDNA group.

    Here's the question. Using both my male cousins results on the Y67 and using the Tip Report the indication is that their common male ancestor has a 70.48 % chance to be at four generations. Since we know they have the same great grandfather shouldn't their common ancestor be 100% or at least near that at three generations. Even at eight generations the estimate is at 94.78 % for a common ancestor. We know their common male ancestor is at three generations.

    Is their a problem with the Tip Report?

  • #2
    You must remember they are using probability based on 1,000s of people. You are basing your question based on two or three people. There is nothing wrong with their report.

    If you have 10 people in a room. 5 of them are 5 feet tall and 5 of them are 6 feet tall, the average height of the 10 people is 5.5 feet. Since none of the people are 5.5 feet tall are you going to say the average is wrong?

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    • #3
      The TiP report assumes that you have NO OTHER EVIDENCE apart from the Y DNA results at the indicated level (Y 67 in this case). You can interpret this as a statement of how likely it is that two men, randomly chosen, who match to the indicated degree are related within a specified number of generations. The statement refers to the percentages you would get if you looked at a very large number of pairs of men. But those probabilities go out the window as soon as you know more, as you do. A better way to view the results, in light of your other paper trail as well as strong genetic evidence, is that there is nothing in the Y DNA evidence to cause you to doubt the autosomal DNA evidence and your paper trail. If, instead, the TiP report told you the odds were only 2 percent, then you would have to reexamine all of your other evidence.

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      • #4
        Thanks for the replies. Now the report makes more sense. On a different note a project leader also pointed out to me that the tip report would give a higher percentage depending on a fast changing marker. For instance with another one of my kits the person has a GD of 3 (at Y111) with several men but the project leader said he was probably closer to one of those men because of a non match on a fast changing marker.

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