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 |
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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 |