See also: Reduced form
When the Cowles Commission introduced the term "reduced form" it was used to define a set of equations where the "left-hand" dependent variables never appeared on the right-hand of the equations, as opposed to the simultaneous equations, where the dependent variable of an equation can appear as an input in other formulas.4
The original distinction between structure and reduced-form was between the underlying system and the direct relationship between observables implied by the system.
Different combinations of structural parameters can imply the same reduced-form parameters, so structural estimation must go beyond the direct relationship between variables.56
Many economists now use the term "reduced form" to mean statistical estimation without reference to a specific economic model. For example, a regression is often called a reduced-form equation even when no standard economic model would generate it as the reduced form relationship between variables.
These conflicting distinctions between structural and reduced form estimation arose from the increasing complexity of economic theory since the formalization of simultaneous equations estimation. A structural model often involves sequential decision-making under uncertainty or strategic environments where beliefs about other agents' actions matter. Parameters of such models are estimated not with regression analysis but non-linear techniques such as generalized method of moments, maximum likelihood, and indirect inference. The reduced-form of such models may result in a regression relationship but often only for special or trivial cases of the structural parameters.
Reiss & Wolak 2007, p. 4282. - Reiss, Peter C.; Wolak, Frank A. (2007). "Chapter 64 Structural Econometric Modeling: Rationales and Examples from Industrial Organization" (PDF). Handbook of Econometrics. Elsevier. doi:10.1016/s1573-4412(07)06064-3. ISBN 978-0-444-50631-3. ISSN 1573-4412. https://web.stanford.edu/group/fwolak/cgi-bin/sites/default/files/files/Structural%20Econometric%20Modeling_Rationales%20and%20Examples%20From%20Industrial%20Organization_Reiss%2C%20Wolak.pdf ↩
Reiss & Wolak 2007, p. 4411. - Reiss, Peter C.; Wolak, Frank A. (2007). "Chapter 64 Structural Econometric Modeling: Rationales and Examples from Industrial Organization" (PDF). Handbook of Econometrics. Elsevier. doi:10.1016/s1573-4412(07)06064-3. ISBN 978-0-444-50631-3. ISSN 1573-4412. https://web.stanford.edu/group/fwolak/cgi-bin/sites/default/files/files/Structural%20Econometric%20Modeling_Rationales%20and%20Examples%20From%20Industrial%20Organization_Reiss%2C%20Wolak.pdf ↩
Reiss & Wolak 2007. - Reiss, Peter C.; Wolak, Frank A. (2007). "Chapter 64 Structural Econometric Modeling: Rationales and Examples from Industrial Organization" (PDF). Handbook of Econometrics. Elsevier. doi:10.1016/s1573-4412(07)06064-3. ISBN 978-0-444-50631-3. ISSN 1573-4412. https://web.stanford.edu/group/fwolak/cgi-bin/sites/default/files/files/Structural%20Econometric%20Modeling_Rationales%20and%20Examples%20From%20Industrial%20Organization_Reiss%2C%20Wolak.pdf ↩
Reiss & Wolak 2007, p. 4293. - Reiss, Peter C.; Wolak, Frank A. (2007). "Chapter 64 Structural Econometric Modeling: Rationales and Examples from Industrial Organization" (PDF). Handbook of Econometrics. Elsevier. doi:10.1016/s1573-4412(07)06064-3. ISBN 978-0-444-50631-3. ISSN 1573-4412. https://web.stanford.edu/group/fwolak/cgi-bin/sites/default/files/files/Structural%20Econometric%20Modeling_Rationales%20and%20Examples%20From%20Industrial%20Organization_Reiss%2C%20Wolak.pdf ↩
Keane 2010. - Keane, Michael P. (2010). "Structural vs. atheoretic approaches to econometrics". Journal of Econometrics. 156 (1). Elsevier BV: 3–20. doi:10.1016/j.jeconom.2009.09.003. ISSN 0304-4076. https://doi.org/10.1016%2Fj.jeconom.2009.09.003 ↩