After we have a brief review of the approach, let's take another look. What was of interest was that the range for people responding to a query went from the teens, and below, up to a whopping 83% (Yvonne). The query was posted by Randy Seaver in his Saturday Night Genealogy Fun post at his Genea-Musings blog. Randy, himself, had a number about 53%.
Again, on the approach, the idea is to count from yourself backward through the earlier generations. So, you have two parents; they have two parents, and so forth. So, it's a power of two (minus yourself) that you have each time.
Some generations can have a 100% number, if everyone is known. We usually expect that with the earlier generations (closer to you). As well, if you take your four grand-parents, what you know about their heritage will differ. For some, you may know a lot. For others, you many know little.
What has been noted is that many, with New England ancestry, know a lot about their ancestors. The high number, reported above, was for someone who was from Quebec (Canada).
Fore note: Randy had four columns: possible - #1, sum1; identified - #2, sum2. He reported, for each generation, sum2/sum1 (times 100, to get the percentage value). In the below, what is reported is #2 over #1 (adjusted, accordingly). With this, we can see what we know for each generation.
To the prior table, I added three columns (see image in this post). Each of these will show "Percentages of known, by generation." The first column gives the ratio (converted to percentage) by generation, in toto. In this case, 45.7% of generation-nine ancestors are known (117 of the 256 possible). As one can see, this percentage drops off as we go backward in time. So, too, does the accumulative numbers drop (51.3%, which is 262 of the 511 possible at this generation).
|Percentages by grandparents|
(of which, of course,
there are four)
The next column is the number for the paternal grandfather. Then, we have a column the maternal grandfather.
The first thing to notice is that we have 100%, for these two, out through generation seven. Then, we get the drop off that is expected. But, notice, too, that the percentages are high for a couple of generations, above 80%. After that, the paternal side goes down more quickly.
The big reality is that, after generation eleven, we get a huge drop off. It might be good to compare these generations against the trees of the better-studied individuals (rich and famous, for whom genealogists like work).
Caveat: Generation 10, in this case, is for someone who was born toward the middle of the 1900s. Since then, trees for many might be talking generation 12, or more, for the same ancestor (immigrant).
Remarks: Modified: 08/14/2015