van Driel 2008

Methods	ITS with segmented regression analysis with monthly data points
Participants	Belgian National Health Insurance members
Interventions	Two policies issued: March 2001: H2As became available without restrictions; March 2003: two PPIs became available without resrictions
Outcomes	Utilization and costs
Notes	4 month transition period (2 months before and 2 months after) were included retrospectively
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 reported
Other bias	Low risk	No other source of bias detected
Intervention independent of other changes	High risk	"an evidence report that was distributed to all physicians and pharmacists in September 2004. Several events and interactions interfering with the policies have been discussed, but many other events may also have played a role."
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	Objective data obtained from an administrative database with standard collection rules.