Lichtenstein 2000.

Methods	Setting: community, USA Recruitment: via electric utility mailing to identify households with smokers and low radon concentrations
Participants	1006 smokers in 714 households, average cpd 20
Interventions	No face‐to‐face contact ∙ Standard Environmental Protection Agency leaflet on risks of radon ∙ Pamphlet highlighting risk of smoking in low concentrations of radon, with tips for quitting, or not smoking indoors ∙ Second bullet above plus up to 2 brief proactive telephone calls. All groups received standard letter with radon results
Outcomes	Abstinence at 12 months, sustained at 3 months and 12 months Validation: none
Notes	2 vs 1, self‐help vs other control 3 contributes to telephone counselling review (Stead 2013b) Cluster‐randomisation; 54% of smokers lived with another smoker Intraclass correlation for sustained abstinence was .010; analyses did not correct for this
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Randomised by household; method not described
Allocation concealment (selection bias)	Unclear risk	No details given
Blinding (performance bias and detection bias) All outcomes	Low risk	Self‐reported outcomes from participants not blinded to treatment condition, but the arms included in this analysis had similar levels of intensity with no personal contact, so differential misreport judged unlikely
Incomplete outcome data (attrition bias) All outcomes	Low risk	80% of households reached at 3 months and 12 months; no difference across conditions Missing treated as smoking