Table 1. Risk factors in relation to body mass index: differences in mean, variability and skewness estimated by GAMLSS (n = 6007).
| Risk factor | % | NO distribution | BCCG distribution | |||
|---|---|---|---|---|---|---|
| Mean | SD | Median | CoV | Skewness* | ||
| Female (ref) | 52.4% | 28.1 | 6.1 | 26.9 | 0.22 | 1.10 |
| Male | 47.6% | 28.7 | 4.6 | 28.2 | 0.16 | 0.75 |
| Unadjusted difference, % (SE) | 1.9 (0.5) | –27.6 (1.8) | 4.1 (0.4) | –23 (1.8) | 0.48 (0.11) | |
| Adjusted† difference, % (SE) | 2.2 (0.5) | –27.4 (1.8) | 4.4 (0.4) | –22.6 (1.8) | 0.54 (0.11) | |
| Non-manual (ref) | 36.3% | 27.7 | 5.2 | 27 | 0.19 | 1.15 |
| Manual social class | 63.7% | 28.8 | 5.5 | 28 | 0.19 | 0.90 |
| Unadjusted difference, % (SE) | 4.0 (0.5) | 6.1 (1.9) | 4.4 (0.5) | 6 (1.9) | 0.39 (0.11) | |
| Adjusted† difference, % (SE) | 3.8 (0.5) | 5.5 (1.9) | 4.3 (0.4) | 5.6 (1.9) | 0.40 (0.12) | |
| Physically active (ref) | 73% | 28.1 | 5.2 | 27.4 | 0.19 | 0.97 |
| Inactive | 27% | 29.1 | 6.0 | 28.3 | 0.21 | 0.94 |
| Unadjusted difference, % (SE) | 3.3 (0.6) | 13.5 (2.1) | 2.9 (0.5) | 10.4 (2.1) | 0.08 (0.12) | |
| Adjusted† difference, % (SE) | 3.3 (0.6) | 12.1 (2.1) | 3.1 (0.5) | 9.3 (2.1) | 0.12 (0.12) | |
*
Skewness is estimated as the Box-Cox power (that is, the power required to transform the outcome to a normal distribution); differences are the absolute difference in Box-Cox power in each subgroup estimated by GAMLSS. GAMLSS estimates multiple distribution moments simultaneously; thus, differences may not exactly correspond to descriptive comparisons reported above.
†
Estimates mutually adjusted for sex, social class and physical inactivity.
NO: normal distribution; BCCG: Box-Cox Cole and Green distribution: SD: standard deviation; CoV: coefficient of variation; GAMLSS: Generalized Additive Models for Location, Scale and Shape; SE, standard error.