Depends how good of a filter the police are using. Even if they are only targeting people who are 10 times as likely to be users as the general population in th

Depends how good of a filter the police are using. Even if they are only targeting people who are 10 times as likely to be users as the general population in the above example, that only brings the accuracy to about 84%. And I'd wager their filtering isn't that good. What exactly are they using to determine who is a likely user? Are those people really more likely at all, and if so, how much? I expect it would be highly optimistic to even assume a person targeted by police is even three times as likely as the general population to be in possession of drugs, which would only be about 60%