What I am hoping to learn in this Question is the correct terminology and any tools available for determining what I will try to describe below.
Firstly, I know that I will never know all my ancestors because all known ancestors have ancestors who may be unknown.
However, if I know my 2 parents, 4 grandparents, 8 great-grandparents then I would say I know 100% of them to three generations back. By "know" let's assume just knowing their name qualifies as knowing them.
If, I then know 3 of my 16 great-great-grandparents and none of my 3 greats-grandparents and beyond, then I think I could score my known ancestors by adding up like this:
- 50% because I know both parents
- 25% because I know all grandparents
- 12.5% because I know all great-grandparents
- 3/16 of 6.25% because I know only 3 of my 16 great-great-grandparents (fortunately I actually know all of them and lots beyond)
This gives me a score of 50 + 25 + 12.5 + ((3*6.25)/16) = 88.67%
As you can see this score will asymptote towards 100% but can never reach it because each successive generation that is revealed contributes only half the percentage of the previous one.
I guess my question is: "Does anyone know a name for what I describe above, and do any genealogy packages provide the calculation of this percentage as a function?"
(I use Family Tree Maker and Ancestry.com so that is where I have looked without success so far)
In response to some answers/comments about the over-weighting of parents and other recent ancestors in this measure, my thinking is that the weighting given to them may actually be appropriate. My reasoning is that when a parent is unknown you lose the chance to know half of your ancestors. Similarly, not knowing a grandparent knocks out 25%. I think it may actually be a strength not a weakness - we just need to be clear about what the measurement tells us.