Characteristics of the study population at age one year (white children).

ETS: environmental tobacco smoke*Attack group: "Did she smoke in the year this child was born?"; Whistling group: "Did she smoke during the pregnancy with this child?"† The categories cover the following Townsend Deprivation Index intervals: more affluent: [-6.222, -1.397]; average: [-1.396, 2.828]; more deprived: [2.829, 11.072]‡ Age at end of education >16 years (mother or father)§ Chi squared tests (except for Age: Wilcoxon rank-sum test)Characteristics of the study population at age one year (white children).