How well do you know your interviewees?

How much can you know about your job candidates? Looking at the cover letter, resume, a couple phone interviews and in-person interviews later, you have spent less than 8 hours in total with that person. Can you really figure out if someone is great and a good fit just from this?

For start ups, it seems trite to say that you only want to work with the smartest, best people, and accidentally turn down really great people on occasion because of the high screening process. Google seems to skew heavily towards people with high GPA's from prestigious schools, and screen with notoriously difficult questions. I tend to believe that companies like Google are looking at the wrong stats. It appears that in one study, a typical job interview improved chances of selecting the best candidate by less than 2%. Sabermetrics, as described in Moneyball is really a great read on this topic.

For start ups, it's more important to know what people have done during school than what they've studied. Also, an interview can not replace or guide people to figure out the performance of a particular candidate. I think trial hirings make much more sense than locking into a full year with someone. Marc Andreessen states that you're doing great if 70% of your hires work out. Wouldn't it be better if you gave people a baby several week project to test them and make sure you're hiring the right person?