The future of data analysis. Annals of Mathematical Statistics 33 (1), (1962), page 13.
Variant: "An approximate answer to the right question is worth a great deal more than a precise answer to the wrong question." "as the renowned statistician John Tukey once reportedly said," according to Super Freakonomics page 224.
“Even if we can never quantify [satisfaction or happiness]… as precisely as we currently quantify GNP,… perhaps it is better to be vaguely right than precisely wrong.”
Herman E. Daly and Joshua Farley, in Ecological Economics: Principles and Applications. (2003), page 234. quoted in Beyond GDP Measuring progress, true wealth, and the well-being of nations http://ec.europa.eu/environment/beyond_gdp/key_quotes_en.html, European Commission:Environment
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Herman E. Daly 17
American economist 1938Related quotes

“It is better to be roughly right than precisely wrong.”
Not attributed to Keynes until after his death. The original quote comes from Carveth Read and is:
It is better to be vaguely right than exactly wrong.
Logic, deductive and inductive (1898), p. 351 http://www.gutenberg.org/files/18440/18440-h/18440-h.htm#Page_351
Misattributed

“Accidents are not accidents but precise arrivals at the wrong right time.”
Being Late http://www.poetrysoup.com/famous/poem/21366/Being_Late
From the poems written in English

“Perhaps it is better to be irresponsible and right, than to be responsible and wrong.”
Source: The Art of Racing in the Rain

“Our beliefs about what we are and what we can be precisely determine what we can be”