Table 1.
Descriptive Characteristics of Participants at Age 7 and 15 Years
| Age 7 | Age 15 | |||||
|---|---|---|---|---|---|---|
| n | Mean | SE | n | Mean | SE | |
| Total samplea | 5,641 | 1.21 | 0.02 | 3,202 | 0.97 | 0.02 |
| Complete case (nonsmokers)b | 3,128 | 1.16 | 0.02 | 1,868 | 0.94 | 0.03 |
| Complete case (all)c | – | – | – | 2,015 | 5.76 | 0.59 |
| Sex | ||||||
| Male | 2,906 | 1.19 | 0.02 | 1,584 | 1.02 | 0.03 |
| Female | 2,743 | 1.25 | 0.03 | 1,637 | 0.95 | 0.03 |
| Housing tenure | ||||||
| Owned | 4,480 | 1.13 | 0.02 | 1,807 | 0.93 | 0.02 |
| Private rent | 159 | 1.31 | 0.09 | 67 | 1.06 | 0.12 |
| Subsidized rent | 489 | 1.88 | 0.09 | 130 | 0.88 | 0.16 |
| Crowding index | ||||||
| <1 | 384 | 1.53 | 0.08 | 153 | 1.24 | 0.15 |
| 1–1.5 | 2,254 | 1.21 | 0.03 | 1081 | 0.97 | 0.04 |
| >1.5 | 2,002 | 1.15 | 0.02 | 922 | 0.92 | 0.04 |
| Maternal education | ||||||
| Up to 16 years | 3,099 | 1.27 | 0.02 | 1,751 | 1.03 | 0.03 |
| 18+ years | 1,573 | 1.03 | 0.02 | 1,110 | 0.85 | 0.03 |
| Number of siblings | ||||||
| 0 | 1,725 | 1.16 | 0.03 | 1,008 | 0.93 | 0.03 |
| 1 | 1,777 | 1.18 | 0.03 | 770 | 0.98 | 0.05 |
| 2 | 968 | 1.25 | 0.04 | 248 | 0.98 | 0.10 |
| 3 | 475 | 1.34 | 0.07 | 70 | 1.12 | 0.20 |
| 4+ | 598 | 1.35 | 0.06 | 60 | 1.14 | 0.17 |
| Mother smokes | ||||||
| 0 | 3,341 | 1.07 | 0.01 | 2,313 | 0.92 | 0.02 |
| <10 | 275 | 1.38 | 0.08 | 157 | 1.10 | 0.11 |
| 10+ | 432 | 2.17 | 0.09 | 235 | 1.56 | 0.13 |
Note. Cotinine levels (ng/ml serum) at 7 and 15 years are shown for: a the total number of nonsmoking individuals who have had cotinine measured (i.e., maximum number for the univariable analysis); bthe number of complete case nonsmoking individuals (i.e., who self-report as nonsmokers and are below the cutoff of 9.5ng/ml serum); and, cthe number of individuals on whom complete case data are available (i.e., also including smokers). Cotinine levels are also shown at each level of the predictors used. The geometric means are shown above.