Table 1 Comparisons of basic characteristics of included participants and total participants
|  | Included (n = 2546) | Total (n = 3299) | P * |
|---|---|---|---|
Mean ± SD | |||
 Age (years) | 28.8 ± 3.8 | 29.0 ± 3.7 | 0.04 |
 BMI (kg/m2) a | 21.4 ± 3.0 | 21.5 ± 3.6 | 0.53 |
N (%) | |||
Ethnicity | Â | Â | 0.57 |
 Han | 2515 (99.0) | 3243 (98.8) |  |
 Others | 26 (1.0) | 40 (1.2) |  |
Economic status | Â | Â | 0.94 |
 Difficult/careful/loan | 306 (12.3) | 373 (12.2) |  |
 Fair | 1747 (70.0) | 2125 (69.6) |  |
 Good | 444 (17.8) | 554 (18.2) |  |
Education (years) | Â | Â | 0.66 |
  ≤ 12 | 258 (10.2) | 314 (9.6) |  |
 12–15 | 1970 (77.5) | 2546 (77.6) |  |
  > 15 | 313 (12.3) | 422 (12.9) |  |
Parity b | Â | Â | 0.40 |
 Nulliparous | 2138 (84.0) | 2760 (83.7) |  |
 Parous | 408 (16.0) | 539 (16.3) |  |
Health status | Â | Â | 0.83 |
 Fair/poor/very poor | 578 (22.8) | 729 (23.4) |  |
 Good | 1530 (60.3) | 1869 (60.0) |  |
 Very good | 429 (16.9) | 515 (16.5) |  |
Sleep quality | Â | Â | 0.68 |
 Fair/poor/very poor | 1292 (50.8) | 1602 (51.4) |  |
 Good/very good | 1250 (49.2) | 1514 (48.6) |  |
Smoking | Â | Â | 1 |
 No | 2530 (99.7) | 3255 (99.7) |  |
 Yes | 8 (0.3) | 10 (0.3) |  |
Alcohol use | Â | Â | 1 |
 No | 523 (90.8) | 2311 (90.9) |  |
 Yes | 53 (9.2) | 231 (9.1) |  |