Dobbels 2009.

Study characteristics
Methods	Study design: cluster RCT Study duration: 5 hours Study follow‐up period: 1 year
Participants	Country: Belgium Setting: High School Number: 1328; 6 control schools, 6 intervention schools Age: +17 years Sex: not reported
Interventions	Intervention consisted of a young patient's witness, letter of a mother of a young donor, targeted information, explanation of the law and information on how one can register for organ donor
Outcomes	Primary outcome Intention to register Authors reported intention to register as a donor increased to 40% in intervention group, while control group remained steady at 25% (RR 1.98, 95% CI: 1.5 to 2.7)
Notes	Author contacted back in 2013 and they reported that they have not published. Author followed up in 2019
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Insufficient information (abstract only)
Allocation concealment (selection bias)	Unclear risk	Insufficient information (abstract only)
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Insufficient information (abstract only)
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Self‐reported questionnaire likely to have low risk of detection bias
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Insufficient information (abstract only)
Selective reporting (reporting bias)	High risk	Numerator denominator not reported for intention to register
Other bias	High risk	Only abstract included