Summary of findings 2. Multilevel educational intervention versus no intervention.

Five‐arm cluster randomised trial
Patient or population: employees Setting: workplaces in several locations in the UK Intervention: education and policy development, at organisational level Comparison: no education
Outcomes	Effect of the intervention	№ of participants (studies)	Quality of the evidence (GRADE)
Bullying assessed with: Self report Follow up: mean 6 months	Insufficient data reported for analysis	1041 (1 study)	⊕⊝⊝⊝ VERY LOW 1
Absenteeism assessed with: organisational data	Insufficient data reported for analysis	1041 (1 study)	⊕⊝⊝⊝ VERY LOW 1
*The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: Confidence interval.
GRADE Working Group grades of evidence High quality: We are very confident that the true effect lies close to that of the estimate of the effect Moderate quality: We are moderately confident in the effect estimate: The true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different Low quality: Our confidence in the effect estimate is limited: The true effect may be substantially different from the estimate of the effect Very low quality: We have very little confidence in the effect estimate: The true effect is likely to be substantially different from the estimate of effect

¹ We would have downgraded the quality of evidence once due to high risk of bias caused by study limitations (lack of blinding and use of self‐reporting instrument) and twice due to imprecision (study conducted in mixed settings and with unclear number of participants). However, once was enough to reach very low quality evidence as we started at low quality evidence because the included studies used a controlled before‐after design. We found no reason to upgrade the quality of the evidence.