I feel very surprised that people like Lance Amstrong or any other atheletes could by pass the drug test so easily for many years until they got caught. Until recently, I read a blog post about the statistics that reveal the truth about this:
Anti-doping tests have a huge false-negative problem. I have been talking about this for years
As it is a huge false-negative problem, most of the time, the dopers will escape it. But if a player tested positive, it is very high likely that they use doping. It is only somebody suspects and request an official legal and expensive process.
And even if you pass 500 doping test is not an impressive as you thought, more here
The anti-doping agencies are so concerned about not falsely accusing anyone that they leave a gigantic hole for dopers to walk through. . . . While we think about Armstrong’s plight, let’s not forget about this fact: every one of those who now confessed passed hundreds of tests in their careers, just like Armstrong did. In fact, fallen stars like Tyler Hamilton and Floyd Landis also passed lots of tests before they got caught. In effect, dopers face a lottery with high odds of winning and low odds of losing. .