From Scientific American: Four Europeans selected for epic Mars isolation study
Phew. This sounds rough. You really have to be of sound mind to spend that much time with the same people in close quarters. In the article there is also a mention of an upcoming simulation of the full 520 day study. I can't even imagine the type of personality they'd be looking for with this.
This is a case where having a same sex, same oriented crew is probably important. Sexual tension would suck. I'm wondering now, though, can you masturbate in space? 15 weeks is a long time to go without, let alone a year and a half.