Goodhart's law summarizes the issue: When a measure becomes a target, it ceases to be a good measure. This more common phrasing is from Cambridge anthropologist Marilyn Strathern in her 1997 paper "'Improving Ratings': Audit in the British University System." However, the "law" is named after English economist Charles Goodhart, whose original formulation in a conference paper presented at the Reserve Bank of Australia in 1975 stated: "Any observed statistical regularity will tend to collapse once pressure is placed upon it for control purposes."
Chapter:
Anything That Can Go Wrong, Will
Section:
Be Careful What You Wish For