Background Generalisability has been reported as a barrier to using evidence in policy making. Little data are available on whether US and Canadian based evidence on cost-sharing and medication adherence is generalizable to international populations. To explore external validity, we compared the impact of two similar cost sharing policies, one in the US and one in Ireland, on medication adherence.
Methods A repeated measures longitudinal study design was employed to measure individual drug adherence before and after the introduction of drug cost-sharing policies. The Irish policy introduced a 50 cent copayment/prescription item in a publicly insured population in 2010. A similar policy occurred in the Massachusetts Medicaid population in 2003. Prescription data were obtained from centrally held pharmacy claims databases; HSE-PCRS, in Ireland and Medicaid Analytical Extract in the US New users of anti-hypertensive, anti-hyperlipidaemic and anti-diabetes drugs entered the cohort 6 months prior to initiation of cost-sharing polices and were followed for 12 months post-policy change. Segmented regression with generalised estimating equations and an autoregressive correlation structure was used.
Results The Irish policy change resulted in a 3.9% (95% CI, 2.91%-5.02%) immediate drop in adherence to anti-hypertensive drugs in Ireland, whereas the US policy did not affect anti-hypertensive adherence. Relative to the US, the Irish population had a 5.3% (95% CI, 3.68% - 6.92%) additional decrease in adherence to anti-hypertensive drugs immediately after the policy change. Adherence to anti-hyperlipidaemic drugs was insignificantly reduced (-0.6235%, 95% CI, - 2.41%-1.16%) immediately post-policy change in the U. S. However, adherence to anti-hyperlipidaemics was reduced in Ireland by 3.4% (95% CI, 2.25%-4.62%). Compared to the US, Irish patients decreased their adherence to anti-hyperlipidaemics by 2.8% (95% CI, 0.673%-4.945%). Adherence to anti-diabetic drugs did not differ internationally post-policy change. There was no evidence for international differences in the long-term impact (12 months) of policy changes.
Conclusion Irish and US populations had different changes in adherence to anti-hypertensive and anti-hyperlipidaemic drugs directly after implementation of cost-sharing policies, with greater reductions in adherence in the Irish population. However, changes in adherence to anti-diabetic drugs were similar between the populations. This study suggests that North American and Canadian evidence may not be automatically internationally generalizable. Rather, the specific attributes of a setting should always be considered before applying evidence to policy. This novel study will be of interest to global policymakers as they seek to develop evidence based cost-sharing policies.
- cross country
- health policy
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