How Accurate is the FTDNA TiP Calculator?
by Ed Ralston

A good test would be to compare TiP results for known cousins to actual genealogy. Some of the cousins in our project fall within the caveat of having few or no mismatches to the mode, and/or having lower level tests. The two graphs shown below are for cousins that have medium to high mismatches to the mode and tested at 111 markers. The green arrow shows the highest odds prediction for generations and the dashed line shows the actual genealogical generation.

Above – actual genealogy, one cousin was seven generations and the other six – so 6.5 total. The prediction was almost perfect.

Below - actual genealogy, one cousin was four generations and the other three – so 3.5 total. Again, the prediction was very accurate.

Conclusion

The FTDNA TiP calculator can be a valuable resource in predicting how far back a common ancestor occurred, when used bearing in mind the limitations of statistical probabilities. Its accuracy using two sets of cousins was quite remarkable.

To quickly evaluate TiP results without doing all the math, check which generation falls closest to the 50% probability level. That is close to the point that has the highest probability for any particular generation.