The attribution is arguably to Raymond Wolfinger who actually said the opposite, "The plural of anecdote is data", supposedly at a seminar at Stanford in the 60's or 70's. It also could be attributed to Roger Brinner, who said it to congress while testifying in 2012. I'd argue that it belongs unattributed, since it makes logical sense and no one ever attributes the phrase "the sky is blue" to anyone either.
