Heckman, J. L. (1999). Causal parameters and policy analysis in economics: A twentieth century retrospective. National Bureau of Economic Research.
Lua i Stíl Chicago (17ú heag.)Heckman, James L. Causal Parameters and Policy Analysis in Economics: A Twentieth Century Retrospective. Cambridge: National Bureau of Economic Research, 1999.
Lua MLA (9ú heag.)Heckman, James L. Causal Parameters and Policy Analysis in Economics: A Twentieth Century Retrospective. National Bureau of Economic Research, 1999.
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