Vachhani 2013.

Methods	ITS analysis Data were not analysed appropriately*
Participants	Patients undergoing neurosurgical procedures at the University of Illinois College of Medicine at Peoria, Illinois, United States of America. A total of 22,743 patients were included, 7286 patients before the intervention and 15,456 patients after the intervention.
Interventions	Implementation of the Universal Protocol surgical safety checklist
Outcomes	Annual incidence of wrong‐site neurosurgical events
Notes	*Data re‐analysed
Risk of bias
Bias	Authors' judgement	Support for judgement
Intervention independent of other changes?	Unclear risk	No information provided on other interventions that might effect this intervention
Shape of the intervention effect pre‐specified?	Low risk	Point of analysis is point of intervention
Intervention unlikely to affect data collection?	Unclear risk	No distinction between intervention and records collected
Knowledge of the allocated interventions adequately prevented during the study	Low risk	Data re‐analysed
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	No reporting of missing data
Selective reporting (reporting bias)	Low risk	Main outcome is measured
Other bias	Low risk	Objective outcome

ITS: interrupted time series.