Table 1.
Demographic characteristics in different subgroups.
| Total | Male | Female | P values | |||
|---|---|---|---|---|---|---|
| Children | Adolescents | Children | Adolescents | |||
| n (%) | 1097 (100) | 239 (21.79) | 298 (27.16) | 237 (21.60) | 323 (29.44) | |
| N (%) | 38600094 (100) | 7468190 (19.35) | 11926998 (30.90) | 6947749 (18.00) | 12257157 (31.75) | |
| Age (years), mean (SD) | 12.79 (3.79) | 8.54 (1.64) | 15.15 (2.23)c*** | 8.70 (1.75)d*** | 15.39 (2.10)c***,e*** | <0.001a |
| Race/ethnicity, N (%) | ||||||
| Non-Hispanic White | 20735553 (53.72) | 4098602.3 (54.88) | 6695143.3 (56.13) | 3409718.6 (49.08) | 6532088.6 (53.29) | <0.001 |
| Non-Hispanic Black | 4470180 (11.58) | 867816.9 (11.62) | 1460253.9 (12.24) | 766690.6 (11.04) | 1375419.0 (11.22) | |
| Mexican American | 6126108 (15.87) | 1141425.9 (15.28) | 1776932.6 (14.90) | 1423325.8 (20.49) | 1784424.1 (14.56) | |
| Other Race | 7268253 (18.83) | 1360345.2 (18.22) | 1994668.1 (16.72) | 1348013.8 (19.40) | 2565225.6 (20.93) | |
| Family PIR, N (%) | ||||||
| PIR<=1 | 9112689 (23.61) | 1770793 (23.71) | 2500823 (20.97) | 1959315 (28.20) | 2881758 (23.51) | <0.001 |
| PIR >1 | 29487405 (76.39) | 5697398 (76.29) | 9426174 (79.03) | 4988434 (71.80) | 9375399 (76.49) | |
| Serum cotinine, N(%)b | ||||||
| <LLOD | 14073182 (36.46) | 2612187 (34.98) | 3416099 (28.64) | 3034115 (43.67) | 5010780 (40.88) | <0.001 |
| >=LLOD | 24526912 (63.54) | 4856003 (65.02) | 8510899 (71.36) | 3913633 (56.33) | 7246377 (59.12) | |
| BMI category, N (%) | ||||||
| Normal weight | 29149987 (75.52) | 6856528.4 (91.81) | 8807098.2 (73.84) | 6262098.2 (90.13) | 7224262.1 (58.94) | <0.001 |
| Overweight | 5213428 (13.51) | 381018.3 (5.10) | 1706794.2 (14.31) | 467642.4 (6.73) | 2657973.5 (21.69) | |
| Obese | 4236679 (10.98) | 230643.6 (3.09) | 1413105.5 (11.85) | 218008.2 (3.14) | 2374921.8 (19.38) | |
| Survey time period | ||||||
| Nov. 1 to Apr. 30 | 17545321 (45.45) | 3559588 (47.66) | 5941689 (49.82) | 2951352 (42.48) | 5092692 (41.55) | <0.001 |
| May 1 to Oct. 31 | 21054773 (54.55) | 3908602 (52.34) | 5985309 (50.18) | 3996397 (57.52) | 7164465 (58.45) | |
| Blood collection, N (%) | ||||||
| Morning | 16730845 (43.34) | 2458553 (32.92) | 5235360 (43.90) | 3033536 (43.66) | 6003396 (48.98) | <0.001 |
| Afternoon | 14155481 (36.67) | 3306334 (44.27) | 4585101 (38.44) | 2304349 (33.17) | 3959697 (32.31) | |
| Evening | 7713768 (19.98) | 1703303 (22.81) | 2106537 (17.66) | 1609864 (23.17) | 2294064 (18.72) | |
Sampling weights were applied for calculation of demographic descriptive statistics and N represents the weighted sample size.
a: Age differences of four subgroups (male children, male adolescents, female children and female adolescents) were tested by Welch’s ANOVA because the four subgroups satisfy approximate symmetry and heteroscedasticity; other differences across four subgroups were tested by Chi-square test.
b: The LLOD of serum cotinine was set at 0.015 ng/mL.
c, d, and e represent the post hoc result of SNK method with the group of Male Children, Male Adolescents, and Female Children, respectively, with ***P<0.001.