[Estimation of secondhand smoke exposure: the impact of question wording]

To analyze the impact of question wording on the self-reported prevalence of secondhand tobacco smoke (SHS) exposure.

A cross-sectional study was conducted on a representative sample of the Spanish population aged ≥16 years. A questionnaire was designed with 14 questions selected from health surveys and generated based on recommendations from experts on tobacco. Exposure prevalences and its 95% confidence interval (95%CI) were estimated based on the question, grouped according to the exposure setting: home, work or school, leisure or public places, and general. Concordance was assessed using the percentage of agreement and the kappa index.

2103 people participated. When assessing exposure at home, the highest prevalence of SHS exposure was obtained when asking about cohabiting smokers (37.9%; 95%CI: 35.6-40.1) and the lowest when including frequency of exposure (10.9%; 95%CI: 9.5-12.3). When assessing exposure at work or school and during leisure time, the highest prevalence was achieved when asking about outdoor exposure (41.6%, 95%CI: 38.8-44.5, and 54.6%, 95%CI: 52.3-57.0, respectively). The highest concordance was obtained when comparing the question assessing overall exposure and the question combining exposure in different indoor settings in the last 7 days (90.6%; 95%CI: 89.2-91.9; kappa: 0.71).

The wording of questions influences the estimated prevalence of SHS exposure in the population. There is an urgent need to reach a consensus on how to assess self-reported SHS exposure.