How Many of My Ancestry Matches have Identical Trees copied between Accounts?

Something I find mildly disappointing with a new DNA match on Ancestry is when I realize that I’ve seen their tree before. The exact same identical tree. I’ll recognize this is the case if I’ve spent some considerable time studying the tree in a previous encounter from an earlier DNA match.

What’s happening is that someone is managing multiple accounts, and Ancestry provides the facility to copy the same tree across accounts. Suppose you match to two kits that have been assigned the same tree. When you click on “View Full Tree” from the pedigree page of both matches, the same tree URL is opened.

The reason I get disappointed is that I’m not going to glean much new insight from the DNA match other than an assumption that they are closely related to whoever they have a tree in common. But how often am I likely to stumble across this phenomenon?

In May 2018 I took a snapshot of information across all my DNA matches, and this included the Tree URLS. I used techniques described here, but I think that the DnaGedcom utility also retrieves the Tree URL to spreadsheets. The data allows me to do a little data mining on my snapshot of Tree URLs.

Question: How Many of my Ancestry Matches have Identical Trees copied between Accounts?

Approximately six thousand of my nine thousand DNA matches have an available tree with at least one visible entry. (The 6K excludes those pesky trees with everybody marked as private). 428 of those 6K have an identical tree with another account. Those 428 matches “should” have 428 trees, but they account for a total of 191 trees instead.
So about 7% of my matches with available trees.

It’s not a lot, but it does have some impact. I wrote before on the number of my matches with available trees. The charts I presented in that post are still correct, but the “usefulness” of a subset of those matches is reduced.

One caveat to these numbers: when a match has not linked their tree but has multiple unlinked trees, my snapshot examined the first tree in their list and ignored any others.

Question: Just How Big does this Tree-Sharing Get?

Within the subset of kits sharing a tree, the vast majority are in pairs i.e two matches sharing a tree.
The highest number of matches sharing the same tree is 8. Octuplets? Well, they all have the same surname.

Here’s the distribution:

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