In the This American Life episode “Cops see it differently, Part Two” there is a story about the Miami Gardens police department that implemented some sort of “frisk all residents” policy. The episode focuses on an unfortunate citizen named Earl who was repeatedly arrested for trespassing at his place of work which eventually became his residence as well. It is terrible, ludicrous story but buried in there is an interesting example of self-poisioning a database.

The town has a population of around 110K. In one year, the police managed to stop and file a field report on 99K residents. Great coverage! Field reports in police departments are useful in a lot of ways - they’re a listing of the citizens who have had contact with the police before. If you’re looking for the kind of person that the police might need to contact in the future - you’d look through the field reports.

By interviewing nearly every citizen the police made the database of field reports nearly unusable. They poisoned the database themselves by making it so that searches had to be super specific to return any kind of usuable list.