Hazlet 2002

Methods	Controlled ITS with monthly data points
Participants	Senior beneficiaries in provincial drug benefit plan, British Columbia, Canada Random sample of 10,000 seniors exposed to reference drug pricing followed for 21 months ‐ 9 months before reference pricing and 12 months after implementation Control was 10,000 members whose 21 months of observation preceded reference pricing
Interventions	Special authority for PPIs (reference pricing for H2RAs)
Outcomes	Health services utilization
Notes	No transition period
Risk of bias
Bias	Authors' judgement	Support for judgement
Incomplete outcome data (attrition bias) All outcomes	Low risk	Any undocumented difference in the proportion of missing data in the administrative datasets pre‐ and post‐intervention is unlikely to overturn study results
Selective reporting (reporting bias)	Low risk	All outcomes listed in the methods section are reported in the results section
Other bias	High risk	Modeling assumptions are strict and unrealistic. Raw data not shown
Knowledge of allocated interventions adequately prevented during the study	Low risk	Outcomes are objective measures of healthcare utilization
Intervention independent of other changes	Low risk	Use of closest cohort in time an attempt to protect against secular change Reference based pricing for H2A implemented at same time as PA for PPIs
The shape of intervention pre‐specified?	Low risk	The date the policy intervention was implemented was used to delineate pre and post policy time periods. Raw data points on outcomes were not shown, only the fitted estimates
Intervention unlikely to affect data collection?	Low risk	Data collection was mostly the same before and after except that PharmaNet introduction coincided with this policy. Some of the continuing growth of costs might have been due to more complete submission of reimbursement claims.