IQ is a measure of different components of intelligence as measured on a standardized test so arranged that exactly half of the people taking it score 100 (the 50-th percentile). When the test is given to a large number of people the distribution of scores resembles a bell curve, with intellectually gifted people falling on the curve's right side and their less fortunate counterparts on the left. By tradition, scores of 140 or better indicate genius, whereas those under 90 suggest impaired mentation. The arguable view of Herrnstein and Murray is that scores to the far left of the median are the human equivalent of sawdust; those to the far right, stardust.