My husband and I have always thought that there should be more negative controls and some planted positives in every batch that is tested. When the lab knows its all athletes I think that they are more likely to be "looking for it" (and some of the tests, like EPO if I understand how they do it correctly, can be a bit up to interpretation). If there were more negative controls, a lab turning out false positives would be easier to spot. If there were some that should be positive (and the exact number should be random and secret) then the lab might not be stretching so hard to find someone who maybe looks, possibly a little positive.