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Background: System factors increasingly are suggested as important yet understudied correlates of nonadherence., Objective: To explore the relationship between healthcare system and prevalence of nonadherence with immunosuppressive regimen by studying variation in nonadherence between European and US kidney transplant recipients and as well as nonadherence in European countries., Methods: We performed a secondary data analysis on data collected in 3 independent cross-sectional studies using comparable methodology including patients from the United States, the Netherlands, Belgium, and Switzerland. Nonadherence was measured using 1 item of the Siegal questionnaire. Patients were categorized as nonadherent if they reported missing a dose of immunosuppression in the last 4 weeks. Analyses were performed by multiple mixed logistic regression, with center as a random effect and clinical and demographical differences between groups as fixed effects., Results: 1563 U.S. and 614 European patients from 3 different countries (Belgium [n=187], the Netherlands [n=85], and Switzerland [n=342]) were included. Prevalence of nonadherence in the United States and Europe was 19.3% and 13.2.%, respectively. This higher nonadherence in US patients was confirmed in a multiple logistic regression analysis (OR = 1.78; 95% CI, 1.10-2.89). Nonadherence differed between Belgium (16%) and the Netherlands (14.1%) (OR = 0.27; 95% CI, 0.09-0.80) and between Belgium and Switzerland (11.4%; OR = 0.17; 95% CI, 0.0-0.42)., Conclusion: This is the first study showing differences in prevalence of nonadherence between European and US patients and among European patients. Further research should aim at unraveling the dynamics explaining these differences.

Self-efficacy is an important determinant of health behavior that can be targeted for intervention. Little effort has been given to the development of valid measures for self-efficacy with medication taking for adherence research. The purpose of this study was to determine the criterion validity of the Long-Term Medication Behavior Self-Efficacy Scale (LTMBSES). Individual patient data from 6 existing adherence studies in transplant, hyperlipidemia, and AIDS/HIV patients (n = 1021) were pooled. Validity was determined by assessing the relation between the LTMBSES score and medication adherence--both self-reported and electronically monitored. A weak relationship was found between the LTMBSES score and adherence, which can possibly be attributed to a ceiling effect, caused by a too homogeneous population and/or a failure of the scale to challenge patients. Generalized Estimating Equations revealed that the total average self-efficacy score predicted reported medication adherence (p < .0001). The Receiver Operating Characteristic curve revealed the area under the curve was 0.67, indicating a significant (p < .0001), but poor predictive capability. Evidence for criterion validity of the Long-Term Medication Behavior Self-Efficacy Scale is not yet convincing. Future research should focus on: (1) validation in a population with a more heterogenous level of adherence, and (2) making the scale more challenging by referring to "always taking the medication without exception."