Also a socio-economic level of agency filter effect. At least a couple percent of test results are false positives. Combine those two and you filter out poorer applicants and lower level, lower income employees. If you need to downsize 5% you can start with drug testing everyone and even if no one uses drugs the high false positive rate will get rid of some employees, now you only have to downsize 2% or something. This also works to reduce spend on welfare type programs and unemployment.