Abstract
Difference-in-differences (DID) is a popular approach in observational and quasi-experimental studies to estimate the effects of a treatment with discrete statuses. In many studies, however, the treatment can have a range of dosages or exposure levels. In our paper, “medical homeness” is a semi-continuous score ranging from 0 to 100 to indicate the extent to which a patient-centered medical home model is achieved. We developed a causal DID approach to estimating the effects of a treatment with semi-continuous dosages. The proposed approach allows for mixed-type designs as well as different propensity models. We applied the proposed approach to evaluate the dosage effect of medical homeness scores on the utilization and quality of children’s health care. We found that there was a roughly linear effect of medical homeness scores on the annual number of visits to doctor offices when medical homeness scores were below 60 points. The number of office visits did not further increase when medical homeness scores were above 60. A similar relationship was found between medical homeness scores and ratings for health care quality.
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References
Abadie, A.: Semiparametric difference-in-differences estimators. Rev. Econ. Stud. 72(1), 1–19 (2005)
American Academy of Pediatrics Medical Home Initiatives for Children With Special Needs Project Advisory Committee and others. Policy statement: organizational principles to guide and define the child health care system and/or improve the health of all children. Pediatrics 113(5 Suppl), 1545 (2004)
Andersen, R.M.: Revisiting the behavioral model and access to medical care: does it matter? J. Health Soc. Behav. 36, 1–10 (1995)
Beal, A., Hernandez, S., Doty, M.: Latino access to the patient-centered medical home. J. Gen. Internal Med. 24(3), 514 (2009)
Bethell, C.D., Read, D., Brockwood, K.: Using existing population-based data sets to measure the american academy of pediatrics definition of medical home for all children and children with special health care needs. Pediatrics 113(Supplement 4), 1529–1537 (2004)
Cohen, J.W., Monheit, A.C., Beauregard, K.M., Cohen, S.B., Lefkowitz, D.C., Potter, D., Sommers, J.P., Taylor, A.K., Arnett III, R.H.: The medical expenditure panel survey: a national health information resource. Inquiry 33, 373–389 (1996)
Conley, T.G., Taber, C.R.: Inference with difference in differences with a small number of policy changes. Rev. Econ. Stat. 93(1), 113–125 (2011)
Damiano, P.C., Momany, E.T., Tyler, M.C., Penziner, A.J., Lobas, J.G.: Cost of outpatient medical care for children and youth with special health care needs: investigating the impact of the medical home. Pediatrics 118(4), e1187–e1194 (2006)
Dickens, M.D., Green, J.L., Kohrt, A.E., Pearson, H.A.: The medical home. Pediatrics 90(5), 774–774 (1992)
Domino, M.E., Humble, C., Lawrence Jr., W.W., Wegner, S.: Enhancing the medical homes model for children with asthma. Med. Care 47(11), 1113–1120 (2009)
Ferrari, S., Cribari-Neto, F.: Beta regression for modelling rates and proportions. J. Appl. Stat. 31(7), 799–815 (2004)
Fisher, E.S.: Building a medical neighborhood for the medical home. N. Engl. J. Med. 359(12), 1202–1205 (2008)
Fu, A.Z., Dow, W.H., Liu, G.G.: Propensity score and difference-in-difference methods: a study of second-generation antidepressant use in patients with bipolar disorder. Health Serv. Outcomes Res. Methodol. 7(1–2), 23–38 (2007)
Han, B., Yu, H., Friedberg, M.W.: Evaluating the impact of parent-reported medical home status on children’s health care utilization, expenditures, and quality: a difference-in-differences analysis with causal inference methods. Health Serv. Res. 52(2), 786–806 (2017)
Hastie, T.J. (ed.): Generalized additive models. In: Statistical Models in S. Routledge, New York (2017)
Hirano, K., Imbens, G.W.: The propensity score with continuous treatments. In: Shewhart, W.A., Wilks, S.S., Gelman, A., Meng, X. (eds.) Applied Bayesian Modeling and Causal Inference from Incomplete-Data Perspectives (2005)
Homer, C.J., Klatka, K., Romm, D., Kuhlthau, K., Bloom, S., Newacheck, P., Van Cleave, J., Perrin, J.M.: A review of the evidence for the medical home for children with special health care needs. Pediatrics 122(4), e922–e937 (2008)
Imai, K., Van Dyk, D.A.: Causal inference with general treatment regimes: generalizing the propensity score. J. Am. Stat. Assoc. 99(467), 854–866 (2004)
Lechner, M.: The estimation of causal effects by difference-in-difference methods. Found. Trends Econom. 4(3), 165–224 (2011)
Li, Q., Racine, J.S.: Nonparametric Econometrics: Theory and Practice. Princeton University Press, Princeton (2007)
MacCallum, R.C., Zhang, S., Preacher, K.J., Rucker, D.D.: On the practice of dichotomization of quantitative variables. Psychol. Methods 7(1), 19 (2002)
Rittenhouse, D.R., Shortell, S.M.: The patient-centered medical home: will it stand the test of health reform? JAMA 301(19), 2038–2040 (2009)
Rittenhouse, D.R., Thom, D.H., Schmittdiel, J.A.: Developing a policy-relevant research agenda for the patient-centered medical home: a focus on outcomes. J. Gen. Internal Med. 25(6), 593–600 (2010)
Romaire, M.A., Bell, J.F.: The medical home, preventive care screenings, and counseling for children: evidence from the medical expenditure panel survey. Acad. Pediatrics 10(5), 338–345 (2010)
Romaire, M.A., Bell, J.F., Grossman, D.C.: Health care use and expenditures associated with access to the medical home for children and youth. Med. Care 50, 262–269 (2012)
Rosenbaum, P.R.: The consquences of adjustment for a concomitant variable that has been affected by the treatment. J. R. Stat. Soc. Ser. A (General) 147, 656–666 (1984)
Rosenbaum, P.R., Rubin, D.B.: The central role of the propensity score in observational studies for causal effects. Biometrika 70(1), 41–55 (1983)
Sia, C., Tonniges, T.F., Osterhus, E., Taba, S.: History of the medical home concept. Pediatrics 113(Supplement 4), 1473–1478 (2004)
Slusky, D.J.: Significant placebo results in difference-in-differences analysis: the case of the acas parental mandate. East. Econ. J. 43(4), 580–603 (2017)
Stange, K.C., Nutting, P.A., Miller, W.L., Jaén, C.R., Crabtree, B.F., Flocke, S.A., Gill, J.M.: Defining and measuring the patient-centered medical home. J. Gen. Internal Med. 25(6), 601–612 (2010)
Stevens, G.D., Seid, M., Pickering, T.A., Tsai, K.-Y.: National disparities in the quality of a medical home for children. Maternal Child Health J. 14(4), 580–589 (2010)
Strickland, B., McPherson, M., Weissman, G., Van Dyck, P., Huang, Z.J., Newacheck, P.: Access to the medical home: results of the national survey of children with special health care needs. Pediatrics 113(Supplement 4), 1485–1492 (2004)
Strickland, B.B., Jones, J.R., Ghandour, R.M., Kogan, M.D., Newacheck, P.W.: The medical home: health care access and impact for children and youth in the United States. Pediatrics 127, 604–611 (2011)
Stuart, E.A., Huskamp, H.A., Duckworth, K., Simmons, J., Song, Z., Chernew, M.E., Barry, C.L.: Using propensity scores in difference-in-differences models to estimate the effects of a policy change. Health Serv. Outcomes Res. Methodol. 14(4), 166–182 (2014)
Yang, L., Tsiatis, A.A.: Efficiency study of estimators for a treatment effect in a pretest-posttest trial. Am. Stat. 55(4), 314–321 (2001)
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This study was funded by the Grant R21HD078881 from Eunice Kennedy Shriver National Institute of Child Health & Human Development and by the Grant R01HS023336 from the Agency for Healthcare Research and Quality.
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Appendix
Appendix
Properties 1 to 3 are simply by the definition of \({\mathcal {G}}\), \(r^\delta \), and R.
Proof of Property 4
For any \(\zeta \ge 0\) and by iterative expectations,
By the ignorability assumption, the last expression is equal to
Since \(r^a\) is fully determined by \({\mathcal {G}}\), the last expression is equal to \(\int _0^\zeta r^a \text {d}a= P(d \le \zeta | {\mathbf {X}}).\)□
Proof of Property 5
By Property 2,
Then following essentially the same technique in Theorem 2 in Hirano and Imbens (2002), we first show \(f(Y_1(\delta ) - Y_0 | d=\delta , r^\delta =s) = f(Y_1(\delta ) - Y_0 | r^\delta =s).\)
Given \(s \ne 0\),
In addition,
Therefore, \(f(Y_1(\delta ) - Y_0 | d=\delta , r^\delta =s) = f(Y_1(\delta ) - Y_0| r^\delta =s)\).
Revisit the last expression in (17),
□
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Han, B., Yu, H. Causal difference-in-differences estimation for evaluating the impact of semi-continuous medical home scores on health care for children. Health Serv Outcomes Res Method 19, 61–78 (2019). https://doi.org/10.1007/s10742-018-00195-9
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DOI: https://doi.org/10.1007/s10742-018-00195-9