This quiz is taken almost verbatim from Jeff Atwood's exercise in his article "How Good an Estimator Are You?" , which in turn is based on an excerpt from Steve McConnell's book Software Estimation: Demystifying the Black Art.

This exercise was McConnell's way of showing people that we are usually overconfident estimators.

In an ideal world, if you were asked to provide a 90% confidence interval for the 10 questions in this quiz, you should get about 9 correct (meaning the true answer falls within your provided range). But this is rarely the case. People tend to make their ranges too narrow, and this results in fewer correct answers than expected.

In McConnell's surveys, the average number of correct answers was 2.8 and only 2 percent of quiz takers score 8 or more correct answers. He concluded that most people's intuitive sense of "90% confident" is actually closer to "30% confident."

I decided to make this quiz after I found Jeff's article mentioned in a Hacker News thread. In the results page, I added a histogram with the current results.

If you're into fun cognitive science experiments, check out these other experiments.