Question

When a measure becomes a target it ceases to be a good measure

Answer 1

Goodhart's law is an adage named after economist Charles Goodhart, which has been phrased by Marilyn Strathern as "When a measure becomes a target, it ceases to be a good measure."[1] One way in which this can occur is individuals trying to anticipate the effect of a policy and then taking actions that alter its outcome.