Table 1 Characteristics of participants by the frequency and duration of second-hand smoke exposure.

From: Associations of second-hand smoke exposure with hand eczema and atopic dermatitis among college students in China

Variable Category Total Frequency of smoke exposure (day/week) Duration of smoke exposure (years)
0 1  ≥ 2  < 2 2–5  ≥ 6
N (%) N (%) N (%) N (%) N (%) N (%) N (%)
Study site Changsha 5017 3817 (76.1) 783 (15.6) 417 (8.3) 3683 (73.4) 376 (7.5) 958 (19.1)
Wuhan 5602 4452 (79.5) 820 (14.6) 330 (5.9) 4350 (77.6) 430 (7.7) 822 (14.7)
Xiamen 4206 3224 (76.7) 694 (16.5) 288 (6.8) 3100 (73.7) 300 (7.1) 806 (19.2)
Urumqi 2922 2421 (82.9) 261 (8.9) 240 (8.2) 2522 (86.3) 155 (5.3) 245 (8.4)
Hohhot 2382 1971(82.7) 226 (9.5) 185 (7.8) 1890 (79.3) 142 (6.0) 350 (14.7)
Students’ hometown region North 3605 2962 (82.2) 397 (11.0) 246 (6.8) 2785 (77.3) 229 (6.3) 591 (16.4)
Northeast 631 524 (83.0) 76 (12.0) 31 (5.0) 476 (75.4) 44 (7.0) 111 (17.6)
East 4466 3431 (76.8) 723 (16.2) 312 (7.0) 3455 (77.4) 281 (6.3) 730 (16.3)
Central 4244 3265 (76.9) 673 (15.9) 306 (7.2) 3238 (76.3) 337 (7.9) 669 (15.8)
South 1395 1005 (72.0) 245 (17.6) 145 (10.4) 1013 (72.6) 112 (8.0) 270 (19.4)
Southwest 1802 1398 (77.6) 274 (15.2) 130 (7.2) 1295 (71.9) 164 (9.1) 343 (10.9)
West 3986 3300 (82.8) 396 (9.9) 290 (7.3) 3283 (82.4) 236 (5.9) 467 (11.7)
Age (years)   18.3 ± 0.8 18.3 ± 0.8 18.2 ± 0.7 18.3 ± 0.7 18.3 ± 0.8 18.2 ± 0.7 18.2 ± 0.7
Body mass index (kg/m2)   21.3 ± 3.5 21.2 ± 3.4 21.4 ± 3.6 21.7 ± 3.8 21.3 ± 3.5 21.5 ± 3.6 21.5 ± 3.6
Gender Male 10,283 7816 (76.0) 1526 (14.8) 941 (9.2) 7825 (76.1) 858 (8.3) 1600 (15.6)
Female 9846 8069 (81.9) 1258 (12.8) 519 (5.3) 7720 (78.4) 545 (5.5) 1581 (16.1)
Ethnicity Han 16,222 12,566 (77.5) 2414 (14.9) 1242 (85.1) 12,263 (75.6) 1208 (7.4) 2751 (17.0)
Other 3907 3319 (85.0) 370 (9.5) 218 (5.6) 3282 (84.0) 195 (5.0) 430 (11.0)
Annual family income (CNY)  < 10,000 2169 1828 (84.3) 219 (10.1) 122 (5.6) 1796 (82.8) 123 (5.7) 250 (11.5)
10,001 to 30,000 4377 3541 (80.9) 564 (12.9) 272 (6.2) 3403 (77.7) 319 (7.3) 655 (15.0)
30,001 to 50,000 3468 2754 (79.4) 464 (13.4) 250 (7.2) 2636 (76.0) 282 (8.1) 550 (15.9)
50,001 to 99,999 4416 3409 (77.2) 660 (15.0) 347 (7.9) 3336 (75.5) 317 (7.2) 763 (17.3)
100,000 to 199,999 4063 3126 (76.9) 620 (15.3) 317 (7.8) 3128 (77.0) 269 (6.6) 666 (16.4)
 ≥ 200,000 1636 1227 (75.0) 257 (15.7) 152 (9.3) 1246 (76.2) 93 (5.7) 297 (18.1)
Family structure Core family 14,028 11,086 (79.0) 1933 (13.8) 1009 (7.2) 10,968 (78.2) 910 (6.5) 2150 (15.3)
Single parent 1288 1035 (80.3) 167 (13.0) 86 (6.7) 1031 (80.1) 107 (8.3) 150 (11.6)
Live with custodians other than parents 459 362 (78.9) 65 (14.1) 32 (7.0) 347 (75.6) 42 (9.2) 70 (15.2)
Extended family 4354 3402 (78.1) 619 (14.2) 333 (7.7) 3199 (73.5) 344 (7.9) 811 (18.6)
Smoking (active) No 19,834 15,735 (79.3) 2713 (13.7) 1386 (7.0) 15,355 (77.4) 1358 (6.9) 3121 (15.7)
Yes 295 150 (50.8) 71 (24.1) 74 (25.1) 190 (64.4) 45 (15.3) 60 (20.3)
Alcohol drinking No 19,228 15,312 (79.6) 2596 (13.5) 1320 (6.9) 14,935 (77.7) 1316 (6.8) 2977 (15.5)
Yes 901 573 (63.6) 188 (20.9) 140 (15.5) 610 (67.7) 87 (9.7) 204 (22.6)
Physical activity (min/week) No 8471 6808 (80.4) 1095 (12.9) 568 (6.7) 6584 (77.7) 510 (6.0) 1377 (16.3)
1 to 419 4251 3309 (77.8) 630 (14.8) 312 (7.3) 3268 (76.9) 344 (8.1) 639 (15.0)
 ≥ 420 7407 5768 (77.9) 1059 (14.3) 580 (7.8) 5693 (76.9) 549 (7.4) 1165 (15.7)
ADHD No 19,540 15,483 (79.2) 2675 (13.7) 1382 (7.1) 15,155 (77.5) 1361 (7.0) 3024 (15.5)
Yes 589 402 (68.2) 109 (18.5) 78 (13.2) 390 (66.2) 42 (7.1) 157 (26.7)
History of asthma No 19,826 15,652 (79.0) 2746 (13.8) 1428 (7.2) 15,317 (77.3) 1388 (7.0) 3121 (15.7)
Yes 303 233 (76.9) 38 (12.5) 32 (10.6) 228 (75.2) 15 (5.0) 60 (19.8)
History of allergic rhinitis No 17,857 14,245 (79.8) 2358 (13.2) 1254 (7.0) 13,881 (77.7) 1233 (6.9) 2743 (15.4)
Yes 2272 1640 (72.2) 426 (18.7) 206 (9.1) 1664 (73.2) 170 (7.5) 438 (19.3)
History of eczema No 19,404 15,366 (79.2) 2643 (13.6) 1395 (7.2) 15,043 (77.5) 1344 (6.9) 3017 (15.5)
Yes 725 519 (71.6) 141 (19.5) 65 (9.0) 502 (69.2) 59 (8.1) 164 (22.6)
  1. ADHD attention deficit/hyperactivity disorder.