The problem ratings in Tactics Trainer are based solely upon how well users have fared against them. If a 1500-level player is stumped by a 1500-level puzzle, the player loser points and the puzzle gains points -- probably something like -15 / +15.
If several high-level players make a silly mistake on the same problem, its rating can jump up several dozen points despite not being any harder than when it was first created. This can lead to problems being "overrated". The converse situation can lead to "underrated" problems.
Is it just me, or are the Tactics Trainer problems much more difficult than they used to be? Last summer when I was much weaker, I climbed over 2300 on Tactics Trainer; now I'm several hundred points lower, despite my tactics skills (as measured on other sites and in OTB games) being much stronger. Anyone have similar experiences? Tough problems are good for me -- I'm not complaining about that. But are the ratings in line with the actual difficulty level, or in line with previous rating levels on Tactics Trainer?