I've also read that teenage girls are as effective as professionally trained therapists...
All kinds of therapists or just traditional psychoanalysts? The efficacy of cognitive behavioral therapy is supposed to have strong empirical support. I wouldn't be very surprised if it turned out that most of that support is critically flawed but I also wouldn't be surprised if the study you're referring to was behind the times.
Dunno, it's just something that I remember hearing once. I couldn't find a source.
I did manage to come across the name for this effect: Dodo Bird Verdict.
A piece I saw that Benjamin Todd adapted from THINK's module on charity assessment. Some of you may recall the network's recent launch.
cipergoth said that it should be emphasised that this isn't a trick question where the answer is they all worked or none did.
I thought Round 2 would have no effect and expected Round #5 to have no effect not a negative one, I got 6 out of 8 correct. How well did you do?
I recommend checking out the links and references. Gwern's comment there was also interesting.