Just as “How much has a bank borrowed?” is a good rule of thumb only when the banks aren’t trying to meet this target, “How many patients can get an appointment in forty-eight hours?” is probably a good rule of thumb for judging the overall quality of doctor surgeries that don’t know they’re being judged on it. “How many ambulances arrive within eight minutes?” is likely an excellent proxy for how well ambulance services are being run, provided they aren’t actually trying to meet that target. But as soon as we formalize a rule of thumb into a target, it becomes a source of distortion.
