Table 2.
The properties of different weight variables at age 12 years in 402 boys and 383 girls in the Fels Longitudinal Study
| Mean (SD) | Sex difference in the meana | Sex difference in the SDb | Skewness | Correlation with age | Correlation with height | Variance explained by heightc | |
|---|---|---|---|---|---|---|---|
| Estimate (P value) | % | ||||||
| Raw data | |||||||
| Weight (kg) | 42.976 (9.530) | 2.324 (<0.001) | 0.942 (0.045) | 1.120 (<0.001) | 0.045 (0.209) | 0.693 (<0.001) | 44.6 |
| Internal Z-scores | |||||||
| Computed using sample mean and SD | 0.000 (0.999) | 0.000 (>0.999) | 0.000 (>0.999) | 1.134 (<0.001) | 0.042 (0.241) | 0.680 (<0.001) | 43.4 |
| According to a FLS referenced | −0.012 (0.995) | −0.064 (0.368) | 0.035 (0.488) | 0.032 (0.711) | 0.043 (0.229) | 0.712 (<0.001) | 46.3 |
| External Z-scores | |||||||
| According to the CDC reference | 0.030 (0.996) | −0.097 (0.174) | 0.066 (0.190) | 0.043 (0.623) | 0.010 (0.771) | 0.711 (<0.001) | 46.2 |
| Indices | |||||||
| BMI (kg/m2) | 18.516 (3.066) | 0.505 (0.020) | 0.297 (0.056) | 1.115 (<0.001) | −0.004 (0.910) | 0.347 (<0.001) | 19.2 |
| Weight-for-heightp (kg/m∼3)e | 11.444 (1.818) | 0.878 (<0.001) | 0.310 (<0.001) | 1.054 (<0.001) | −0.037 (0.303) | 0.046 (0.202) | 2.3 |
| Conditional size measures | |||||||
| Unstandardized residuals from weight (kg) regressed on height (m)e | 0.000 (6.868) | 0.000 (>0.999) | 0.868 (0.012) | 1.007 (<0.001) | −0.046 (0.194) | 0.000 (>0.999) | 0.0 |
| Standardized residuals from weight (kg) regressed on height (m)e | 0.000 (1.001) | 0.000 (>0.999) | 0.000 (0.994) | 1.033 (<0.001) | −0.043 (0.224) | 0.000 (0.998) | 0.0 |
Computed as the mean for girls minus the mean for boys so that a positive value indicates a higher mean in girls compared with boys. P values are from t-tests.
Computed as the SD for girls minus the SD for boys so that a positive value indicates a higher SD in girls compared with boys. P values are from variance ratio tests.
Computed using the formula (1 − sqrt(1 − r2)) × 100, where r is the correlation with height.
The FLS reference was constructed by applying sex-stratified LMS models to all weight data collected between birth and age 18 years (1,509 participants, 31,121 observations).
Computation was sex stratified.
BMI body mass index, CDC Centers for Disease Control and Prevention, FLS Fels Longitudinal Study, LMS lambda-mu-sigma, SD standard deviation.