Table 4

Consistency of study design with key quality criteria for interrupted time series

1. Intervention occurred independently of other changes over time.	The statistical analyses indicate that a change occurred just after the publication of the newspaper articles—this is reflected in the stepwise change seen at the time, and the absence of changes observed in the control series. It is possible that the postintervention trend change may have been facilitated by additional interventions. However, these additional interventions may themselves have been motivated by the newspaper articles.
2. Intervention was unlikely to affect data collection.	Data collection for the outcomes was not related to the intervention. Data were obtained from a population-level pharmaceutical dispensing database (the Ontario Drug Benefit database) which includes complete prescription data for all Ontario residents of nursing homes.
3. The primary outcome was assessed blindly or was measured objectively.	The prescribing outcomes are based on objective prescription dispensing data collected from the Ontario Drug Benefit database.
4. The primary outcome was reliable or was measured objectively.	The Ontario Drug Benefit database has been previously validated for research purposes; it is populated based on objective data from dispensing pharmacies. All medication outcomes of interest are captured in this database for the population of interest.
5. The composition of the data set at each time point covered at least 80% of the total number of participants in the study.	The data are complete at the population level for the jurisdiction of Ontario. Within nursing homes in Ontario, there are legislative requirements to complete the Resident Assessment Instrument, including documentation of nursing home date of admission and discharge and this was used to create the cohort for this study. Transparent and objective exclusion criteria on the cohort were applied to ensure an ability to assign a prescriber to each resident. As described in online supplementary appendix 1, after exclusion criteria were applied, a total of 153 263 resident episodes were reduced to 120 009 resident episodes and all of the eligible episodes at each time point were used in the analysis.
6. The shape of the intervention effect was prespecified.	Within Ontario nursing homes, medication dispensing occurs typically on a 1–2 week basis in nursing homes but residents may not be reassessed by physicians weekly unless there is a change in their status; monthly reassessments are more common. We prespecified that changes would take 4–6 weeks to occur, allowing enough time for reassessment and implementation of changes. We then tested our prespecified change point using goodness-of-model-fit criteria.
7. A rationale for the number and spacing of data points was described.	Our 30-month study period with monthly intervals was considered adequate to conduct the analysis given the fact that these data were assessed at the population level (ie, include all nursing home residents in Ontario) with minimal variation in the month-to-month prescribing data, and covered more than 120 000 nursing home resident care episodes across 636 nursing homes. Choosing weekly time intervals would have provided many more data points, but this would have been an artificial attempt at increasing the number of observations at the expense of adding unnecessary random variation, and would not have altered our conclusions. Conversely, quarterly time intervals may not have adequately captured turnover of residents.
8. The study was analysed appropriately using time series techniques.	We used segmented regression and accounted for autocorrelation.