OBJECTIVES. The goals were (1) to develop an index measure of environmental tobacco smoke based on parent self-report of smoking behaviors and (2) to determine whether the index score was associated with children's present and future cotinine levels.
METHODS. Data were drawn from a community intervention for inner-city children with persistent asthma (N = 226; response rate: 72%). Measures of child salivary cotinine levels and parent self-reported environmental tobacco smoke-related behaviors were obtained at baseline and 7 to 9 months later. To develop the index score, we used a 15-fold cross-validation method, with 70% of our data, that considered combinations of smoke exposure variables and controlled for demographic features. We chose the most parsimonious model that minimized the mean square predictive error. The resulting index score included primary caregiver smoking and home smoking ban status. We validated our model with the remaining 30% of the data. Analysis of variance and multivariate analyses were used to determine the association of the index score with children's cotinine levels.
RESULTS. Fifty-four percent of children with asthma lived with ≥1 smoker, and 51% of caregivers reported a complete home smoking ban. The children's mean baseline cotinine level was 1.55 ng/mL (range: 0.0–21.3 ng/mL). Children's baseline and follow-up cotinine levels increased as scores on the index measure increased. In a linear regression, the index score was significantly positively associated with children's cotinine measurements at baseline and 7 to 9 months later.
CONCLUSION. An index measure with combined information regarding primary caregiver smoking and household smoking restrictions helped to identify children with asthma with the greatest exposure to environmental tobacco smoke and could predict which children would have elevated cotinine levels 7 to 9 months later.