I Still Haven't Figured Out the Entirety of the Algorithm ...

 ... at Backgammon Galaxy, but I think I've reverse engineered one part of how it calculates "error rating."

After 400-odd matches (of which, as of a few minutes ago, I've now won exactly 1/3 -- I'm winning more than half these days), I've noticed a very specific trend, and emulated that trend to see if it produced the result I anticipated. It does.

The trend:

I've noticed that many players -- including some pretty highly rated ones -- seem to play a "strategy" of "if there's a single checker you can hit, hit it no matter what the situation, and hope for the best."

In a match this morning, an opponent had seven checkers either on the bar or in my home area, and almost all of them got on the bar by taking out singles of mine while he had singles scattered in his home area that my rolls to get off the bar took out.

I've also noticed that these players seem to get lower error ratings. Which means if you beat them, you don't gain any rating points. But if they happen to win, they do. In the aforementioned match, I ended up winning ... and gaining no rating points.

I played several matches using that "strategy" -- just take out the other guy's checkers, with no regard for getting my own checkers home or seeing to their safety -- and scored lower error ratings than usual. Of course, I lost most of the matches, but I got rating points for the matches I won and didn't lose rating points for the matches I lost. In fact, that probably accounts for the majority of the change in my rating over the last couple of weeks, during which I went from sub-700 to 1,000+.

Something in the algorithm seems to treat taking out a single as inherently less "erroneous" and producing greater "equity," even when doing so is an insanely dumb move.

I've started making a habit of looking at win/loss ratios instead of ratings when I think about clicking on another player's game offering. They seem to be a better indicator of whether I'm going to actually get challenged to play well, or just spend all my time on "let's see who can take out the most checkers, and hey, eventually there will accidentally/incidentally be a winner."