The original formulation by economist Charles Goodhart (1975):
“Any observed statistical regularity will tend to collapse once pressure is placed upon it for control purposes.”
The pithier version you’re paraphrasing is Marilyn Strathern’s 1997 reformulation:
“When a measure becomes a target, it ceases to be a good measure.”
Strathern’s version is the one most people quote — it’s cleaner than Goodhart’s original.
Fact-Check Notes
No factual issues found. Both attributions check out: Charles Goodhart’s 1975 formulation (from his paper/lecture on UK monetary policy) and Marilyn Strathern’s 1997 reformulation (“‘Improving ratings’: audit in the British university system”) are correctly dated and correctly attributed — Strathern’s phrasing is indeed the more widely quoted of the two. No [[wikilinks]] are present in this file, so there is nothing to audit for link validity or relevance.