Schneeweiss 2004

Methods	Controlled ITS with repeated measures analysis with monthly data points
Participants	Senior and low income beneficiaries in provincial drug benefit plan, British Columbia, Canada N=53 pairs of clusters of doctors in British Columbia matched by size of location and number of patients. Policy implementation group n=449 patients affected by policy, policy exempt group n=386 patients. Observational cohort N=4624 patients (excluding n=386 in control goup)
Interventions	Restricted reimbursement for nebulizers, doctors had to request exemption
Outcomes	Drug use, health services utilization, durg costs
Notes	Control group contaminated by announcing policy change to all doctors (including control doctors) therefore cluster randomized controlled trial component of this study was excluded
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	"We randomly assigned one cluster of each pair to either the policy implementation group or the policy exempted control group. Randomising isolated but matched clusters of doctors minimised the risk of contamination and reduced imbalances owing to chance."
Allocation concealment (selection bias)	High risk	"The non‐compliance resulted from a change that Pharmacare made to the protocol at the last minute, which can be avoided in future policy trials. Wanting to underscore the independence of the evaluation from the government, Pharmacare cautiously sent letters announcing the policy change six weeks in advance to all doctors in the province. Control doctors were not told of their exemption until they received a separate letter from the investigators two weeks later. Many control doctors either overlooked the second letter or decided to switch patients to inhaler drugs in anticipation of the new policy."
Incomplete outcome data (attrition bias) All outcomes	Low risk	All outcomes reported and adjusted
Selective reporting (reporting bias)	Low risk	All relevant outcomes in the methods section are reported in the results section
Other bias	Low risk	Considered by authors: "in the first month after the policy was implemented doctors reduced their office hours to meet budget caps at the end of the fiscal year, possibly more than in the previous year. The randomised analysis was protected from this bias since the concurrent control patients were equally as affected as the intervention patients.
Baseline outcome measurements similar	Low risk	"The historical control groups showed some seasonal variation, with higher use of respiratory drugs in the six months preceding 1 March compared with the subsequent six months."
Baseline characteristics similar	Low risk	"The baseline distributions of age, sex, drug use, comorbidity score, and use of healthcare did not differ between the randomised groups (table 1; all P values > 0.1). The observational cohorts had slightly more women than the randomised groups (62% v 59%). Otherwise the observational cohorts were comparable to each other."
Knowledge of allocated interventions adequately prevented during the study	Low risk	"We used de‐identified data from the databases of British Columbia’s Ministry of Health "
Study adequately protected against contamination?	High risk	Control doctors were notified of the policy change 2 weeks before recieving a letter informing them of their exemption.
Intervention independent of other changes	Low risk	We first adjusted for seasonality separately, using each of the two historical control cohorts.A significant interaction would mean that changes in end point trends because of the policy were different from the control cohorts, independent of seasonality.
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	"We used de‐identified data from the databases of British Columbia’s Ministry of Health to monitor use of and expenditure..."