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.
