Apparently humans are more competitive when there are fewer of us competing for the prize:
Students taking standardized tests in more crowded venues got lower scores. Students asked to complete a short general-knowledge test as fast as possible to win a prize if they were in the fastest 20 percent completed it faster if they were told that they were competing against 10 people rather than 100.
Intuitively, I guess that we feel more likely to win if we have to beat fewer people. With a smaller group to compete against, the probability of having a low ability group is greater than with a larger sample where ability is likely to be closer to the population distribution. I was going to class this as behavioural economics, but I suppose it just shows our intuitions to be more rational than I expected!