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Econometrics may be defined as the quantitative analysis of actual economic phenomena based on the concurrent development of theory and observation, related by appropriate methods of inference.

"Report of the evaluative committee for Econometrica". Paper by Paul Samuelson, Tjalling Koopmans, and Richard Stone. Econometrica - journal of the Econometric Society, pp. 141-146, 1954.
Econometrics may be defined as the quantitative analysis of actual economic phenomena based on the concurrent development of theory and observation, related by appropriate methods of inference.