In the course of preparing for my presentation on when to appeal, I asked Matt Pollack for whatever statistics the SJC had on the probabilities of success on appeal. Here they are:
As this shows, the chance of any kind of alteration in the judgment is about 1 in five. The only type of appeal where the chances of prevailing are higher than not is, unsurprisingly, worker's comp, because those appeals are discretionary - like the U.S. Supreme Court, if you are granted cert, odds are you will win.
As you can see by the second slide, the overall results are also skewed by the low level of success in criminal, family and child protection matters. If you look at the "other" bar or the 80B-8 bar, which I think gives a better feel for an ordinary civil appeal, the odds go to about 1 in three.