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Table 1 Demographic characteristics of the study sample (N = 49,507)

From: Changes in distributions of waist circumference, waist-to-hip ratio and waist-to-height ratio over an 18-year period among Chinese adults: a longitudinal study using quantile regression

  1993 1997 2000 2004 2006 2009 2011 P*
Sample size 5442 7546 7686 7571 7465 7363 6434  
Male (%) 2638 (48) 3801 (50) 3703 (48) 3660 (48) 3581 (48) 3542 (48) 3056 (47)  
Female (%) 2804 (52) 3745 (50) 3983 (52) 3911 (52) 3884 (52) 3821 (52) 3378 (53)  
Age (years) 38.62 (30.00,46.54) 40.20 (30.56,48.82) 42.44 (33.05,50.85) 45.14 (35.83,53.25) 46.26 (37.47,54.37) 46.94 (38.86,55.61) 48.62 (40.77,56.86) < 0.001
Smoke         < 0.001
No (%) 3528 (65) 4978 (66) 5180 (67) 5052 (67) 5061 (68) 4997 (68) 4423 (69)  
Yes (%) 1914 (35) 2565 (34) 2502 (33) 2516 (33) 2403 (32) 2366 (32) 2011 (31)  
Drink         < 0.001
No (%) 3406 (63) 4647 (62) 4883 (64) 4943 (65) 4907 (66) 4722 (64) 4170 (65)  
Yes (%) 2036 (37) 2889 (38) 2788 (36) 2626 (35) 2557 (34) 2641 (36) 2264 (35)  
Energy intake (1000 kcal/d) 2.373 (1.959,2.836) 2.428 (2.019,2.929) 2.326 (1.913,2.797) 2.258 (1.841,2.747) 2.290 (1.845,2.821) 2.163 (1.779,2.622) 2.053 (1.637,2.557) < 0.001
Total physical activity(100METs/d) 2.11 (1.00,3.37) 2.60 (1.28,4.56) 2.07 (1.03,4.00) 1.73 (0.80,3.46) 1.72 (0.76,3.33) 1.75 (0.84,3.28) 1.85 (0.90,3.25) < 0.001
Education level         < 0.001
None/primary (%) 2902 (53) 3692 (49) 3321 (43) 2974 (39) 2778 (37) 2678 (36) 2279 (35)  
Middle school (%) 1651 (30) 2369 (31) 2575 (34) 2665 (35) 2592 (35) 2754 (37) 2422 (38)  
Senior/above (%) 888 (16) 1472 (20) 1782 (23) 1930 (25) 2093 (28) 1931 (26) 1733 (27)  
Marital status         < 0.001
Unmarried (%) 625 (11.5) 965 (12.8) 809 (10.5) 582 (7.7) 466 (6.2) 375 (5.1) 267 (4.1)  
Married (%) 4682 (86.0) 6318 (83.7) 6578 (85.6) 6655 (87.9) 6668 (89.3) 6581 (89.4) 5779 (89.8)  
Divorced (%) 21 (0.4) 46 (0.6) 68 (0.9) 92 (1.2) 93 (1.2) 128 (1.7) 138 (2.1)  
Other (%) 114 (2.1) 217 (2.9) 231 (3.0) 242 (3.2) 238 (3.2) 279 (3.8) 250 (3.9)  
Individual income (Yuan) 2595.48 (1502.49,4392.02) 3564.56 (2055.24,5714.71) 4432.20 (2355.11,7263.67) 5261.33 (2693.60,9672.23) 6024.26 (2872.05,10,962.58) 8889.46 (4832.47,15,685.91) 11,036.93 (5860.76,18,708.16) < 0.001
Urbanicity index 43.94 (32.75,60.88) 51.21 (35.18,66.90) 55.19 (42.69,76.76) 58.74 (44.27,81.11) 61.85 (47.26,82.31) 64.09 (51.07,84.69) 67.99 (51.63,86.24) < 0.001
WC (cm) 74.0 (70.0,80.0) 77.0 (71.0,83.2) 78.0 (72.0,85.0) 80.0 (74.0,87.0) 80.0 (74.0,87.5) 82.0 (75.0,89.2) 83.0 (76.0,90.4) < 0.001
Height (cm) 160.0 (154.1166.0) 160.4 (154.9166.8) 160.8 (155.0,167.2) 161.0 (155.3167.5) 161.2 (156.0,168.0) 161.5 (156.0,168.0) 161.7 (156.0,168.0) < 0.001
HC (cm) 89.0 (85.0,94.0) 91.0 (86.6,96.0) 93.0 (88.0,98.0) 93.0 (88.0,98.0) 93.1 (89.0,98.2) 94.1 (89.5,99.8) 95.0 (90.0,100.0) < 0.001
  1. Continuous variables are expressed as medians (25th percentile, 75th percentile), categorical variables are expressed as frequency (percentages %)
  2. * Chi-square tests for categorical variables and Kruskal–Wallis tests for continuous variables
  3. Abbreviation: WC, waist circumference; HC, hip circumference