predict the best mile time?? Now, most people don't run very much and only a few train at all. If you want to know your "personal best" mile time you need to do a lot of training. Let's say that only 1/20 people in a population bother to do this. We have all of their mile times. Let's say the average is 7:30 and the best is 4:12. The SD is... I don't know, let's say, 1 min. Now based on the fact that this is only 5% of the population can we predict the world record mile time if EVERY woman trained until she could run her personal best?