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Table 1 Descriptive characteristics of premenopausal women by menstrual cycle regularity (KNHANES, 2010–2012)

From: Factors associated with menstrual cycle irregularity and menopause

  Total (n = 4788) Regular (n = 4103) Irregular (n = 685)
  n % SE n % SE n % SE
Age, years
 19 to < 30 1157 30.6 1.0 943 28.9 1.0 214 39.7 2.3
 30 to <40 1737 31.6 0.9 1568 33.4 1.0 169 21.6 1.8
 ≥ 40 1894 37.8 0.9 1592 37.7 1.0 302 38.7 2.1
Residence
 Rural 601 13.8 1.4 504 13.4 1.4 588 15.7 2.3
 Urban 4187 86.2 1.4 3599 86.6 1.4 97 84.3 2.3
Household income, quartiles
 I 1130 27.7 0.9 968 27.7 1.0 162 27.5 2.3
 II 1171 24.7 0.8 1024 25.4 0.9 147 21.2 1.9
 III 1203 23.9 0.8 1009 23.2 0.9 194 27.4 2.2
 IV 1236 22.6 0.9 1060 22.6 0.9 176 22.6 2.0
 Missing data 48 1.1 0.2 42 1.1 0.2 6 1.2 0.7
Marital status
 Married 3563 69.2 1.0 3090 70.6 1.0 473 61.4 2.2
 Not married 1225 30.8 1.0 1013 29.4 1.0 212 38.6 2.2
Educational level
 Elementary school and below 144 3.2 0.3 104 2.8 0.3 40 5.9 1.0
 Middle school 251 5.8 0.4 186 5.1 0.4 65 9.6 1.3
 High school 2183 48.4 1.0 1848 47.6 1.1 335 53.0 2.4
 University and above 2202 42.3 1.0 1959 44.3 1.1 243 31.2 2.2
 Missing data 8 0.2 0.1 6 0.2 0.1 2 0.4 0.3
Smoking status
 Non-smoker 4264 87.2 0.6 3663 87.6 0.6 601 85.2 1.6
 Ex-smoker 208 4.8 0.4 181 4.9 0.4 27 4.5 1.0
 Current smoker 316 8.0 0.5 259 7.6 0.5 57 10.3 1.5
Secondhand smoking
 None 1359 27.3 0.8 1174 27.6 0.9 185 25.3 2.0
 < 1 h 211 4.8 0.4 183 4.9 0.4 28 4.5 1.1
 ≥ 1 h 392 9.8 0.6 334 9.9 0.6 58 9.1 1.3
 Missing data 2826 58.1 0.9 2412 57.6 1.0 414 61.1 2.2
Cigarettes per day
 Non-smoker 4264 87.2 0.6 3663 87.6 0.6 601 85.2 1.6
 < 20 cigarettes 478 11.7 0.6 400 11.3 0.6 78 13.7 1.6
 ≥ 20 cigarettes 44 1.1 0.2 38 1.1 0.2 6 1.1 0.5
 Missing data 2 0.0 0.0 2 0.0 0.0    
Age at smoking initiation
 Non-smoker 4264 87.2 0.6 3663 87.6 0.6 601 85.2 1.6
  < 20 years 242 6.5 0.5 199 6.2 0.5 43 8.1 1.3
 ≥ 20 years 282 6.3 0.4 241 6.2 0.5 41 6.7 1.2
Pack-year
 Non-smoker 4264 87.2 0.6 3663 87.6 0.6 601 85.2 1.6
 Above the median (2.5 pack-years) 249 6.0 0.4 206 5.6 0.4 43 8.0 1.3
 Below or equal to the median (2.5 pack-years) 257 6.4 0.5 220 6.3 0.5 37 6.4 1.2
 Missing data 18 0.4 0.1 14 0.4 0.1 4 0.4 0.2
Alcohol consumption
 None 604 12.0 0.6 520 12.1 0.6 84 11.5 1.5
 ≤ 1 time per month 2085 43.2 0.9 1783 42.7 0.9 302 45.9 2.1
 2–4 times a month 1164 24.6 0.8 1003 25.2 0.8 161 21.2 1.9
 2–3 times a week 456 9.7 0.6 396 9.9 0.6 60 8.8 1.3
 ≥ 4 times a week 100 2.5 0.3 81 2.3 0.3 19 3.4 1.0
 Missing data 379 8.0 0.5 320 7.8 0.6 59 9.2 1.4
Body mass index
 0 to < 18.5 kg/m2 443 10.0 0.5 388 10.2 0.6 55 9.3 1.3
  18.5 to < 23 kg/m2 2521 51.0 1.0 2211 52.2 1.0 310 44.8 2.4
  23 to < 25 kg/m2 807 17.0 0.6 689 17.1 0.7 118 16.0 1.6
  25 to < 30 kg/m2 811 17.2 0.7 662 16.3 0.8 149 22.2 1.8
 ≥ 30 kg/m2 191 4.5 0.4 143 4.0 0.4 48 7.3 1.3
 Missing data 15 0.3 0.1 10 0.3 0.1 5 0.5 0.2
Perceived stress
 Little 396 8.0 0.5 347 8.2 0.5 49 7.1 1.2
 A little 2847 58.3 0.9 2477 59.3 0.9 370 52.8 2.3
 Much 1304 28.2 0.8 1086 27.4 0.9 218 32.1 2.1
 Very much 241 5.5 0.4 193 5.0 0.4 48 8.0 1.2
Modifiable risk factor scorea
 0 450 9.38 0.52 399 9.8 0.58 51 7.04 1.24
 1 2452 54.6 0.97 2134 55.5 1.02 318 49.8 2.48
 2 925 21.3 0.77 787 21.1 0.86 138 22.4 1.92
 ≥ 3 568 14.72 0.7 454 13.7 0.7 114 20.7 1.99
  1. aThe given scores were summed and categorized based on smoking status, obesity level, and drinking frequency. The given score of each variable was as follows: 0 point each for non-smokers, underweight to overweight  (0 to < 25 BMI), and nondrinkers; 1 point each for ex-smokers, obesity I (25 to < 30), and 1–4 times per month alcohol consumption frequency; and 2 points each current smoker, obesity II (≥30 BMI), and ≥ 2 times a week alcohol consumption frequency