Syzygy tables and endgame occurance or frequency

Hi, I've just been reading about endgame tablebases, and doing a few experiments with syzygy 7 piece endings. I enjoyed looking at these online articles, and forum topics... https://www.chessprogramming.org/Endgame_Tablebases https://www.chessprogramming.org/Syzygy_Bases ftp://ftp.chessdb.cn/pub/syzygy/7men/ http://talkchess.com/forum3/viewtopic.php?f=2&t=69309 http://talkchess.com/forum3/viewtopic.php?t=68117 I've noticed a few people coming to the conclusion that it's perhaps efficient to use a subset of the syzygy 7 piece tables, in conjunction with complete syzygy 6 piece tables. And that it's valuable if you know which are most commonly required syzygy 7 piece tables. I've seen the terms 'occurrence ranking' and 'endgame frequency' used to describe this idea. One author suggested the most occuring 7 piece endings to be: 1) KRPPvKRP 2) KBPPvKBP 3) KPPPvKPP With KRPPvKRP occuring 30%, and the others around 5% each. There was also a suggestion made that there is a difference between human and engine games. My question is… does anyone know a good reference or study of 'occurrence ranking' for endgames, in particular 7 piece endgames? My apologies if this is commonly known, and I didn't find it. Thanks for help.

Rook endings are far more common than bishop endings or pawn endings. The reason is that the side which is behind will not trade rooks.