Dijkstra 1998a.

Methods	Setting: community, Netherlands Recruitment: newspaper adverts; not selected by level of motivation to quit
Participants	1546 smokers, 59% female, average age 40, average cpd 20.3
Interventions	No face‐to‐face contact ∙ Letter with information on positive outcomes of quitting (OC) ∙ Letter with information on skills for quitting (SE) ∙ Letter with outcomes and skills information (BO) All letters computer‐generated reports of 4 to 7 pages, personalised and tailored from baseline questionnaire ∙ No information (CO)
Outcomes	12‐month sustained abstinence at 14 months; self‐report by postal questionnaire Validation: none; participants told that a sample would be tested for CO levels
Notes	1 and 2 and 3 vs 4 in tailored materials since 2014 (previously in main comparison) Results sensitive to the outcome used; no difference in point prevalences
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Randomised; method not described
Allocation concealment (selection bias)	Unclear risk	No details given
Blinding (performance bias and detection bias) All outcomes	High risk	No biochemical validation used; control group knew other participants receiving an intervention
Incomplete outcome data (attrition bias) All outcomes	Low risk	64% responded at 14 months; no differences across groups Attrition predicted by perceived pros of quitting and intention to quit but not different between groups Denominator in meta‐analysis based on all randomised