Gedmatch question

[Sara291]

I'm looking into two possible sets of distant grandparents to my children. Comparing them from Gedmatch, Ancestry and FTDNA. I've compared two matches and found a common set of grandparents as well as another set and found a common set of grandparents all from the same tiny area in Sweden (even close farms). Trying to work down from there. As each has 7-10 children it seems. When looking at Gedmatch two of the 4 cousins I'm looking into are listed (one from each set if that makes sense). He matches 4 people. Out of those 4 they each match with one of the other 4. Anyways Gedmatch has a Gen suggestion of 4.0 for one and 4.2 for the other cousin I'm looking at. This may be a dumb question but does that suggest they share a ancestor 4 generations back (including them)?
When I look at the 4.2 the common ancestor I see (shared with another match) shares a great great great grandparent. Also possibly the great great but I'm not certain. These great great great grandparents I talk about had two children and I'm trying to figure when my children's decended from.

Anyways can someone explain the generation suggestion of 4.2? Or any input.

[John McCoy]

The listed number of generations is simply an estimate based on an algorithm of some kind. There appear to be different algorithms in use by different vendors and/or web sites. They are apparently based on real data, but probably not on very large sample sizes.

Obviously, nobody is exactly 4.2 generations removed from someone else. It's the same idea as the statement that the "average" American family has 2.5 children. The methodologies for estimating the number of generations back to a common ancestor are apparently very rough, because they so often turn out to be off the mark. In particular, whatever FTDNA is doing seems wildly optimistic.

In comparing two matches to see which one is closer, I wouldn't want to put much faith in the generations number unless the two values were very different.

[Dabney Carr]

Gedmatch has a Gen suggestion of 4.0 for one and 4.2 for the other cousin I'm looking at... does that suggest they share a ancestor 4 generations back (including them)?

They are suggesting that they share a common ancestor four generations back, but I believe you start counting with the parents.

0 - Child
1 - Parents
2 - Grandparents
3 - Great Grandparents
4 - Great Great Grandparents

So they are suggesting the nearest common ancestors as great grandparents. In other words, they are also suggesting that the two cousins you are comparing had great grandparents who were siblings.

Again, this is just an estimate. It could go back several generations more or sometimes less, but it is a good starting point for where to look in a family tree.