Background Replication of intervention research is reported infrequently, limiting what we know about external validity and generalisability. The Smoke Free Homes Program, a minimal intervention, increased home smoking bans by United Way 2-1-1 callers in randomised controlled trials in Atlanta, Georgia and North Carolina.

Objective Test the programme's generalisability-external validity in a different context.

Methods A randomised controlled trial (n=508) of English-speaking callers from smoking-discordant households (≥1 smoker and ≥1 non-smoker). 2-1-1 Texas/United Way HELPLINE call specialists serving the Texas Gulf Coast recruited callers and delivered three mailings and one coaching call, supported by an online tracking system. Data collectors, blind to study assignment, conducted telephone interviews 3 and 6 months postbaseline.

Results At 3 months, more intervention households reported a smoke-free home (46.6% vs 25.4%, p<0.0001; growth model intent-to-treat OR=1.48, 95% CI 1.241 to 1.772, p<0.0001). At 6 months, self-reported full bans were 62.9% for intervention participants and 38.4% for controls (OR=2.19). Texas trial participants were predominantly women (83%), single-smoker households (76%) and African-American (65%); half had incomes ≤US$10 000/year (50%). Texas recruitment was <50% of the other sites. Fewer callers reported having a smoker in the household. Almost twice the callers with a household smoker declined interest in the programme/study.

Conclusions Our findings in a region with lower smoking rates and more diverse callers, including English-speaking Latinos, support programme generalisability and convey evidence of external validity. Our recruitment experience indicates that site-specific adjustments might improve recruitment efficiency and reach.

Trial registration number NCT02097914, Results.