Validity of self-reported indicators to assess secondhand smoke exposure in the home

Introduction: Questionnaires are widely used to assess secondhand smoke (SHS) exposure. However, the validity of self-reported SHS exposure indicators has been rarely assessed. We aimed to assess correlations, sensitivity, specificity, and predictive values between self-reported SHS exposure indicators and airborne nicotine concentrations. Methods: We performed a cross-sectional study with a convenience sample of 175 homes in Barcelona and Santiago de Compostela, Spain. Airborne nicotine samples were collected from participants' homes and a self-administered questionnaire was completed on SHS exposure in the home. Spearman correlations coefficients and sensitivity, specificity and predictive values were assessed between self-reported SHS exposure indicators and nicotine concentrations in the home. Results: All self-reported SHS exposure indicators correlated moderately strongly with airborne nicotine concentrations (Spearman correlations coefficient ranging from 0.58 to 0.65). Moreover, sensitivities and negative predictive values between self-reported indicators and the presence of nicotine in the home were below 66.4% while specificities and positive predictive values were over 78.4%. The "number of people usually smoking in the home" showed the best results (r(s) = 0.65, p < 0.001; sensitivity = 50.4%, specificity = 95.2%, PPV = 95.0, NPV = 51.3). Conclusions: The self-reported SHS indicators assessed in this study showed moderate and strong correlations, low sensitivities, and high specificities. Among them, the best results were obtained with the "number of people usually smoking in the home".