--- Statistician George E P Box, in "Science and statistics", Journal of the
American Statistical Association 71:791-799, quoted in Holling, C S, Stephen R Carpenter, William A Brock, and Lance H Gunderson, “Discoveries for Sustainable Futures”, Ch. 15 in Gunderson, Lance H and C S Holling, Panarchy: Understanding transformations in human and natural systems, Island Press (2002), p. 409
Wikiquote provides some alternative citations and variations:
"Essentially, all models are wrong, but some are useful."
--- Box, George E. P.; Norman R. Draper (1987). Empirical Model-Building and Response Surfaces, p. 424, Wiley. ISBN 0471810339.
"Remember that all models are wrong; the practical question is how wrong do they have to be to not be useful."
--- Box and Draper, Empirical Model-Building, p. 74
"All models are false but some models are useful."