You're probably right. The percentiles listed so far are of the people who have taken the quiz, not of the population as a whole. And their average self-reported verbal SAT score, so far, is around 700 (out of a perfect 800 score). Compare that to the average US population score of around 500, and it's clear that our test-takers are far more literate than average. As the number of participants increases, there should be more data to separate out percentiles based on different self-reported SAT scores, for example, and we'll be able to use this to generate comparison scores that are more representative of the population as a whole.