The effect of patient satisfaction with pharmacist consultation on medication adherence: an instrumental variable approach
There are limited studies on quantifying the impact of patient satisfaction with pharmacist consultation on patient medication adherence.
Objectives: The objective of this study is to evaluate the effect of patient satisfaction with pharmacist consultation services on medication adherence in a large managed care organization.
Methods: We analyzed data from a patient satisfaction survey of 6,916 patients who had used pharmacist consultation services in Kaiser Permanente Southern California from 1993 to 1996. We compared treating patient satisfaction as exogenous, in a single-equation probit model, with a bivariate probit model where patient satisfaction was treated as endogenous. Different sets of instrumental variables were employed, including measures of patients' emotional well-being and patients' propensity to fill their prescriptions at a non-Kaiser Permanente (KP) pharmacy. The Smith-Blundell test was used to test whether patient satisfaction was endogenous. Over-identification tests were used to test the validity of the instrumental variables. The Staiger-Stock weak instrument test was used to evaluate the explanatory power of the instrumental variables.
Results: All tests indicated that the instrumental variables method was valid and the instrumental variables used have significant explanatory power. The single equation probit model indicated that the effect of patient satisfaction with pharmacist consultation was significant (p<0.010). However, the bivariate probit models revealed that the marginal effect of pharmacist consultation on medication adherence was significantly greater than the single equation probit. The effect increased from 7% to 30% (p<0.010) after controlling for endogeneity bias.
Conclusion: After appropriate adjustment for endogeneity bias, patients satisfied with their pharmacy services are substantially more likely to adhere to their medication. The results have important policy implications given the increasing focus on the roles of pharmacists and regulatory changes in professional scope of practice.
2. Medicare Prescription Drug, Improvement and Modernization Act of 2003, Public Law 108–173—DEC. 8.
3. McCombs JS, Cody M, Besinque, K, Borok G, Ershoff D, Groshen S, Hay J, Johnson K, Nichol MB, Nye MT. Measuring the impact of patient counseling in the outpatient pharmacy setting: the research design of the Kaiser Permanente/USC patient consultation study. Clin. Ther. 1995; 17(6): 1188-1206.
4. Worley MM, Schommer JC, Brown LM, Hadsall RS, Ranelli PL, Stratton TP, Uden DL. Pharmacists’ and patients’ role in the pharmacist-patient relationship: are pharmacist and patients reading from the same relationship script? Res Soc Admin Pharm. 2007;3:47-69.
5. Schommer JC, Pedersen CA, Worley MM, Brown LM, Hadsall RS, Ranelli PL, Stratton TP, Uden DL, Chewning BA. Provision of risk management and risk assessment information: the role of the pharmacist. Res Soc Admin Pharm. 2006;2:458-478.
6. Lonie JM. From counting and pouring to caring: the empathic developmental process of community pharmacists. Res Soc Admin Pharm. 2006;2:439-457.
7. Lee JK, Grace KA, Taylor AJ. Effect of a pharmacy care program on medication adherence and persistence, blood pressure, and low-density lipoprotein cholesterol: a randomized controlled trial. JAMA. 2006;296(21):2563-2571.
8. McCombs JS, Liu G, Shi J, Feng W. Cody M, Parker JP, Nichol MB, Hay JW, Johnson KA, Groshen SL, Nye MT. Kaiser Permanente/USC patient consultation study: change in use and cost of health care services Am J Health-Syst Pharm. 1998; 55:2485-2499.
9. Yuan Y, Hay J, McCombs J. Mortality and hospitalization impacts of pharmacy consultation in ambulatory care. Amer J Manag Care. 2003;9(1):101-112.
10. Paulos CP, Nygren CEA, Celedon C, Carcamo C. Impact of pharmaceutical care program in a community pharmacy on patients with dyslipidemia. Ann Pharmacother. 2005;39:939-943.
11. Tsuyuki RT, Johnson JA, Teo KK, Simpson SH, Ackman ML, Biggs RS, Cave A, Chang WC, Dzavik V, Farris KB, Galvin D, Semchuk W, Taylor JG. For the Study of Cardiovascular Risk Intervention by Pharmacists (SCRIP) Investigators. A randomized trial of the effect of community pharmacist intervention of cholesterol risk management. Arch Intern Med. 2002;162:1149-1155.
12. Gerber RA, Liu G, McCombs, JS. Impact of pharmacist consultations provided to patients with diabetes on healthcare costs in a health maintenance organization. Am J Man Care. 1998;4:991-1000.
13. McLennan DN, Dooley MJ, Brien JE. Beneficial clinical outcomes resulting from pharmacist interventions. J Oncol Pharm Practice. 1999;5(4):184-189.
14. Jaber LA, Halapy H, Fernet M, Tummalapalli S, Diwakaran H. Evaluation of a pharmaceutical model in diabetes management. Ann Pharmacother. 1996;30(3):294-295.
15. Aharony L, Strasser S. Patient satisfaction: what we know about and what we still need to explore. Med Care Res Rev. 1993; 50: 49-79.
16. Renberg T, Lindblad AK, Tully MP. Exploring subjective outcomes perceived by patients receiving a pharmaceutical care service. Res Soc Admin Pharm. 2006;2:212-231.
17. Guirguis LM, Chewning BA. Role theory: literature review and implications for patient-pharmacist interactions. Res Soc Admin Pharm. 2005;1:483-507.
18. Oparah AC, Kikanme LC. Consumer satisfaction with community pharmacies in Warri, Nigeria. Res Soc Admin Pharm. 2006;2:499-511.
19. MacKinnon KJ, Swanson LS (Eds.) Striving beyond patient satisfaction: a road map for pharmacists. Inet Continuing Education. 2005; 9(9): www.InetCE.com [accessed on March 26, 2008].
20. Ownby RL. Medication adherence and cognition: medical, personal and economic factors influence level of adherence in older adults. The Psychiatric Consultant. 2006;61(2):30-35.
21. McClellan MB, Newhouse JP. Overview of the special supplement issue. Health Serv Res. 2000;35:1061-1069.
22. Newhouse JP, McClellan MB. Econometrics in outcomes research: the use of instrumental variables. Annual Review of Public Health. 1998;19:17-34.
23. Greene WH. Econometric Analysis (5th edition). Upper Saddle River, NJ: Prentice Hall, 2003.
24. Wooldridge JM. Econometric Analysis of Cross Section and Panel Data. MIT Press, Cambridge, MA, 2001.
25. Yoo BK, Frick KD. The instrumental variable method to study self-selection mechanism: a case of influenza vaccination. Value in Health. 2006;9(2):114-122.
26. Hay J. Appropriate econometric methods for pharmacoeconometric studies of retrospective claims data: an introductory guide. J Manag Care Pharm. 2005;11(4): 344-348.
27. Johnson KA, Nye M, Hill-Besinque K, Cody M. Measuring the impact of patient counseling in the outpatient pharmacy setting: development and implementation of the counseling models for the Kaiser Permanente/USC patient consultation study. Clin Ther. 1995;17(5):988-1002.
28. Hays RD, Kravitz RL, Mazel RM, Sherbourne CD, DiMatteo R, Rogers WH, Greenfield S. The impact of patient adherence on health outcomes for patients with chronic disease in the medical outcomes study. J Behav Med. 1994;17(4):346-360.
29. Kwon A, Bungay KM, Pei Y, Rogers WH, Wilson IB, Zhou Q, Adler DA. Antidepressant use: concordance between self-report and claims records. Med Care. 2003;41:368-374.
30. Saunders K, Simon G, Bush T, Grothaus L. Assessing the feasibility of using computerized pharmacy refill data to monitor antidepressant treatment on a population basis: a comparison of automated and self-report data. J Clin Epidemiol. 1998; 51(10):883-890.
31. Rickles NM, Svarstad BL. Relationships between multiple self-reported nonadherence measures and pharmacy records. Res Soc Admin Pharm. 2007;3:363-377.
32. Johnson JA, Coons SJ, Hays RD, Pickard AS. Health status and satisfaction with pharmacy services. Am J Managed Care. 1999;5:163-170.
33. Cleary PD, McNeil BJ. Patient Satisfaction as an indicator of quality of care. Inquiry. 1988; 25: 25-36.
34. Christofides L, Stengos T, Swidinsky R. On the calculation of marginal effects in the bivariate probit model. Economics Letters, Elsevier, July 1997; 54(3): 203-208.
35. Smith RJ, Blundell RW. An exogeneity test for a simultaneous equation Tobit model with an application to labor supply. Econometrica. 1986; 54(3): 679-685.
36. Sargan JD. The estimation of economic relationships using instrumental variables. Econometrica. 1958; 26(3): 393-415.
37. Basmann RL. On finite sample distributions of generalized classical linear identifiability test statistics. Journal of the American Statistical Association. 1960; 55(292): 650-659.
38. Staiger D, Stock JH. Instrumental variables regression with weak instruments. Econometrica, 1997. 65(3):557-586.
39. Gurwitz JH, Field TS, Harrold LR, Rothschild J, Debellis K, Seger AC, Cadoret C, Fish LS, Garber L, Kelleher M, Bates DW. Incidence and preventability of adverse drug events among older persons in the ambulatory setting. JAMA 2003; 289(9):1107–1116.
40. Brown LM, Schommer JC, Worley MM. Patient view of pharmacists’ roles in health care: how similar are they to how pharmacists view themselves? Research in Social and Administrative Pharmacy 2007; 3: el0-e11.
41. Larson LN, MacKeigan LD. Further validation of an instrument to measure patient satisfaction with pharmacy services. J Pharm Mark Manage 1994; 8:125-140.
The authors hereby transfer, assign, or otherwise convey to Pharmacy Practice: (1) the right to grant permission to republish or reprint the stated material, in whole or in part, without a fee; (2) the right to print pr epublish copies for free distribution or sale; and (3) the right to republish the stated material in any format (electronic or printed). In addition, the undersigned affirms that the article described above has not previously been published, in whole or part, is not subject to copyright or other rights except by the author(s), and has not been submitted for publication elsewhere, except as communicated in writing to Pharmacy Practice with this document.
Authors retain copyright and grant the journal right of first publication with the work simultaneously licensed under a Creative Commons Attribution License (CC-BY-NC-ND) that allows others to share the work with an acknowledgement of the work's authorship and initial publication in this journal.