Grootendorst 2005

Methods	ITS monthly data points
Participants	Senior beneficiaries in provincial drug benefit plan, British Columbia, Canada
Interventions	Type 2 reference pricing for first line restricted non‐steroidal anti‐inflammatory drugs (NSAIDs) (different NSAIDs considered interchangeable)
Outcomes	Drug costs, drug use
Notes	Pharmacare data aggregated from Feb 1993 to June 2001
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	Low risk	No evidence of other risk of bias including seasonality.
Knowledge of allocated interventions adequately prevented during the study	Low risk	Outcomes are objective measures of healthcare utilization
Intervention independent of other changes	Unclear risk	A moderate upward trend in use of opiates that was almost a mirror image of the decline in NSAID use from 1998 to 2001.
The shape of intervention pre‐specified?	Low risk	The point of analysis is the point of intervention; ie, the date the policy intervention was implemented was used to delineate pre and post policy time periods with adequate data points to capture the shape of the pattern of intervention effect over time
Intervention unlikely to affect data collection?	Low risk	Sources and methods of data collection were the same before and after the intervention however the introduction of PharmaNet at the same time as RP (in Sep 95) caused better capture of drug claims because it eliminated the need for seniors to mail in their drug claims.