Lichtenstein 2008.

Methods	Setting: community, USA Recruitment: via electric utility mailing with offer of radon test kit to identify households with smokers
Participants	1364 households with 1821 smokers, ˜ 18 cpd
Interventions	Factorial design crossing ± brief phone counselling with video self‐help materials All households given A Citizen's Guide to Radon and a letter tailored to results of radon level test ∙ Video (15 minutes) explaining risk of smoking and radon combination, encouraging quitting and/or household smoking bans ∙ No video
Outcomes	Abstinence at 12 months, sustained at 3 months and 12 months Validation: none
Notes	Analyses accounting for clustering of multiple smokers in households reported to yield results generally consistent with simple analyses We were unable to obtain data for arms with and without phone counselling, so the collapsed data contribute to comparisons 1.1.2 and 2.1.2
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	High risk	Responding households sequentially randomised to 4 conditions subject to stratification on radon test status; no true randomisation sequence used
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 all received phone counselling and some self‐help, so performance and detection bias judged to be unlikely
Incomplete outcome data (attrition bias) All outcomes	Low risk	83% of households completed 12 months' assessment; 76% completed both 3 months' and 12 months' assessment