All you clever statistics guys...

In tactics trainer, the pass rate for problems is almost always between 45 and 60%. Very rarely lower than 45 or higher than 60.

I dont think I've ever seen below 40 or over 65, for problems with more than a few hundred attempts.

Seems a little weird to me......

Just a guess.  I think problems here have their own rating.  So if lots of people start solving it, its rating goes down, and now only weaker players see it and people start to fail it more often.

If everyone misses it its rating goes up until people start solving it.

Problems rating changes on every attempt

Yep, ideally the pass rate is around 50 percent.

I've seen one that has hundreds of attempts and only 22% pass rate.

Well, then it must continue to rise. But it will take a long time to have a correct pass rate because the pass rate is an average over all attempts. It means that they gave the problem too low a rating to start with.

There are probably some outliers : very hard and very easy problems. Also new problems with few attempts.

I have seen a problem with a pass rate of 6%. I was one of the others.

http://www.chess.com/tactics/problems?sortby=sequential

The low pass rate ones are ones with multiple moves and a tough final move. So because of the way the scoring works the user gets a decent amount of points for a partial solve (e.g. 7/8), and the problem rating doesn't increase meaning that stronger users still don't see it.

http://www.chess.com/tactics/?id=360641

what is doggy making he doesn't go to bed?

* Raises ball-peen hammer *

I'm also reading this, at 2:30 am

Bloody mosquitos are keeping me awake

ah, I thought South Africa was same hour use Spain is... Maybe the change of hour in the old continent for the winter?

we delayed the clock one hour last week? don't you do so?

Nah, we're GMT+2 all year round