See also, http://en.wikipedia.org/wiki/Goodharts_law http://en.wikipedia.org/wiki/Goodharts_law . There are several take-aways, but the relevant one here is "a

See also, http://en.wikipedia.org/wiki/Goodharts_law http://en.wikipedia.org/wiki/Goodharts_law . There are several take-aways, but the relevant one here is "a metric becomes useless as soon as it is a goal."