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Interaction Effects and Difference-in-Difference Estimation in Loglinear Models


  • John Mullahy


In applied econometric work, analysts are concerned often with estimation of and inferences about interaction effects, e.g. 'Does the magnitude of the effect of z1 on y depend on z2? ' This paper develops tests for and proper interpretation of various forms of interaction effects in one prominent class of regression models loglinear models for which the nature of estimated interaction effects has not always been given due attention. The results obtained here have a direct bearing on the interpretation of so-called difference-in-difference estimates when these are obtained using loglinear models. An empirical example of the impacts of health insurance and chronic illness on prescription drug utilization underscores the importance of these issues in practical settings.

Suggested Citation

  • John Mullahy, 1999. "Interaction Effects and Difference-in-Difference Estimation in Loglinear Models," NBER Technical Working Papers 0245, National Bureau of Economic Research, Inc.
  • Handle: RePEc:nbr:nberte:0245 Note: TWP

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    References listed on IDEAS

    1. Mullahy, John, 1998. "Much ado about two: reconsidering retransformation and the two-part model in health econometrics," Journal of Health Economics, Elsevier, vol. 17(3), pages 247-281, June.
    2. Wedig, Gerard J., 1988. "Health status and the demand for health : Results on price elasticities," Journal of Health Economics, Elsevier, vol. 7(2), pages 151-163, June.
    3. Halvorsen, Robert & Palmquist, Raymond, 1980. "The Interpretation of Dummy Variables in Semilogarithmic Equations," American Economic Review, American Economic Association, vol. 70(3), pages 474-475, June.
    4. James Heckman, 1997. "Instrumental Variables: A Study of Implicit Behavioral Assumptions Used in Making Program Evaluations," Journal of Human Resources, University of Wisconsin Press, vol. 32(3), pages 441-462.
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    1. Bruno Amable & Donatella Gatti & Elvire Guillaud, 2008. "How does Party Fractionalization convey Preferences for Redistribution in Parliamentary Democracies ?," Université Paris1 Panthéon-Sorbonne (Post-Print and Working Papers) halshs-00348878, HAL.
    2. Bauer, Thomas K. & Haisken-DeNew, John P., 2001. "Employer learning and the returns to schooling," Labour Economics, Elsevier, vol. 8(2), pages 161-180, May.
    3. Leandro D’Aurizio & Domenico Depalo, 2016. "An Evaluation of the Policies on Repayment of Government’s Trade Debt in Italy," Italian Economic Journal: A Continuation of Rivista Italiana degli Economisti and Giornale degli Economisti, Springer;Società Italiana degli Economisti (Italian Economic Association), vol. 2(2), pages 167-196, July.
    4. Ciani, E & Fisher, P, 2013. "Dif-in-dif estimators of multiplicative treatment effects," Economics Discussion Papers 8973, University of Essex, Department of Economics.
    5. Hagedoorn, John & Wang, Ning, 2010. "Is there complementarity or substitutability between internal and external R&D strategies?," MERIT Working Papers 005, United Nations University - Maastricht Economic and Social Research Institute on Innovation and Technology (MERIT).
    6. Chiou, Lesley & Tucker, Catherine, 2013. "Paywalls and the demand for news," Information Economics and Policy, Elsevier, vol. 25(2), pages 61-69.
    7. Kamhon Kan & Yen-Ling Lin, 2009. "The labor market effects of national health insurance: evidence from Taiwan," Journal of Population Economics, Springer;European Society for Population Economics, vol. 22(2), pages 311-350, April.
    8. Edith Duclos & Pierre Lefebvre & Philip Merrigan, 2001. "A 'Natural Experiment' on the Economics of Storks: Evidence on the Impact of Differential Family Policy on Fertility Rates in Canada," Cahiers de recherche CREFE / CREFE Working Papers 136, CREFE, Université du Québec à Montréal.
    9. Ina Jäkel, 2014. "Import-push or export-pull? An industry-level analysis of the impact of trade on firm exit," Empirica, Springer;Austrian Institute for Economic Research;Austrian Economic Association, vol. 41(4), pages 747-775, November.
    10. Michael Lechner, 2002. "Mikroökonometrische Evaluation arbeitsmarktpolitischer Massnahmen," University of St. Gallen Department of Economics working paper series 2002 2002-20, Department of Economics, University of St. Gallen.
    11. Lavallée, Emmanuelle & Lochard, Julie, 2015. "The comparative effects of independence on trade," Journal of Comparative Economics, Elsevier, vol. 43(3), pages 613-632.

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    JEL classification:

    • C2 - Mathematical and Quantitative Methods - - Single Equation Models; Single Variables
    • I1 - Health, Education, and Welfare - - Health

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