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Table 1 Characteristics of women born in southeastern China between 1955 and 1985 by 5-year birth cohort

From: Secular trends in age at menarche among women born between 1955 and 1985 in Southeastern China

  1955–60 1961–65 1966–70 1971–75 1976–80 1981–85 Association Trend
  (n = 7 128) (n = 53 245) (n = 309 379) (n = 369 971) (n = 348 356) (n = 79 040) P Value P Value
Age at menarche (yrs), mean (SD) 15.7 (1.5) 15.5 (1.39) 15.1 (1.3) 14.9 (1.3) 14.8 (1.2) 14.7 (1.2) <0.0001* <0.0001
Age at registration (yrs), mean (SD) 36.2 (2.6) 32.3 (2.25) 27.3 (3.3) 25.1 (2.6) 24.4 (2.0) 22.3 (1.1) <0.0001* <0.0001
Region, n (%)        <0.0001 <0.0001
Urban 847 (11.9) 3 902 (7.3) 39 698 (12.8) 51 565 (13.9) 58 740 (16.9) 9 127 (11.6)   
Rural 6 281 (88.1) 49 343 (92.7) 269 681 (87.2) 318 406 (86.1) 289 616 (83.1) 69 913 (88.5)   
Education, n (%)        <0.0001 <0.0001§
High school or above 876 (12.3) 6 195 (11.67) 52 373 (17.0) 78 738 (21.3) 124 960 (35.9) 25 420 (32.3)   
Middle school 2 151 (30.3) 25 278 (47.60) 167 684 (54.4) 232 677 (63.0) 200 758 (57.7) 49 501 (62.8)   
Primary school or less 4 076 (57.4) 21 634 (40.5) 88 225 (28.6) 57 768 (15.7) 22 152 (6.4) 3 897 (4.9)   
Medical health history, n (%)        <0.0001 <0.0001
No chronic diseases 6 854 (96.2) 51 096 (96.0) 298 418 (96.5) 360 774 (97.5) 343 415 (98.6) 78 453 (99.3)   
At least one chronic disease 274 (3.8) 2 149 (4.0) 10 961 (3.5) 9 197 (2.5) 4 941 (1.4) 587 (0.7)   
  1. Missing age at registration, 20; Missing education information, 2 756.
  2. *P value from ANOVA.
  3. P value from linear regression.
  4. P value from Pearson Chi-square test.
  5. P value from Cochrane-Armitage Trend test.
  6. §P value from Mantel-Haenszel test.