Humerfelt 1998.

Methods	Setting: community, Norway Recruitment: from participants in a community survey of men aged 30 to 45 years who had increased risk of obstructive lung disease or lung cancer
Participants	2610 men who smoked with reduced FEV₁ and/or occupational asbestos exposure, average age 37, average cpd 16
Interventions	∙ Mailed self‐help pamphlet (15 pages), emphasising behavioural modification techniques in smoking cessation and recommending an early quit date, accompanied by a letter from a respiratory physician advising of high risk status established by the survey ∙ No intervention
Outcomes	Abstinence at 15 months (point prevalence) Validation: participants in 1 geographical area invited for CO measurement (CO < 10 ppm)
Notes	For meta‐analysis, the number of quitters has been adjusted for the validated rate found in the sample tested (63% in intervention/67% in control) Participants who stopped smoking before receiving materials were included Study authors give 12 months' sustained abstinence rates of 5.6% vs 3.5%, but these rates are based on self‐report by responders
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	Low risk	Control group not aware of intervention received by intervention group; biochemical validation conducted in subset of participants; no significant difference in misreport detected (1 intervention, 2 control)
Incomplete outcome data (attrition bias) All outcomes	Low risk	Loss to follow‐up greater in the intervention group (17%) than in the control group (8%) The probability of responding to the follow‐up questionnaire was inversely related to baseline cpd consumption in the intervention group but not in the control group Losses included as smokers