Table 2 A secular trends in age at menarche among 1,275,000 women in Yunnan province according to birth cohorts

 Han

14.085 ± 1.361 (14.029–14.142)

13.820 ± 1.240 (13.811–13.828)

13.715 ± 1.19 4(13.711–13.719)

13.595 ± 1.144 (13.592–13.599)

13.298 ± 1.039 (13.256–13.340)

(− 0.7876)(− 0.8574,-0.7178)

<0.0001

 Yi

14.180 ± 1.498 (14.008–14.352)

13.939 ± 1.368 (13.914–13.964)

13.834 ± 1.303 (13.824–13.843)

13.678 ± 1.234 (13.669–13.688)

13.408 ± 1.159 (13.305–13.511)

(− 0.7725)(− 0.9604,-0.5846)

<0.0001

 Dai

14.019 ± 1.352 (13.646–14.391)

13.813 ± 1.302 (13.763–13.864)

13.655 ± 1.250 (13.639–13.672)

13.544 ± 1.211 (13.527–13.560)

12.979 ± 1.143 (12.791–13.168)

(− 1.0397)(− 1.4207,-0.6587)

<0.0001

 Bai

14.413 ± 1.696 (14.166–14.660)

14.029 ± 1.366 (13.986–14.071)

13.898 ± 1.342 (13.879–13.917)

13.711 ± 1.280 (13.690–13.732)

13.053 ± 1.038 (12.711–13.394)

(− 1.3604)(− 1.9239,-0.7969)

<0.0001

 Miao

14.202 ± 1.471 (13.901–14.503)

13.962 ± 1.275 (13.909–14.016)

13.802 ± 1.182 (13.782–13.822)

13.552 ± 1.091 (13.538–13.567)

13.280 ± 0.946 (13.222–13.339)

(− 0.9218)(− 1.1336,-0.71)

<0.0001

 Hani

14.329 ± 1.527 (14.079–14.579)

14.152 ± 1.456 (14.103–14.201)

13.950 ± 1.353 (13.929–13.970)

13.563 ± 1.14 1(13.545–13.580)

13.255 ± 1.087 (13.049–13.460)

(− 1.0742)(− 1.4114,-0.737)

<0.0001

 Zhuang

14.000 ± 1.449 (13.680–14.320)

13.868 ± 1.358 (13.816–13.920)

13.732 ± 1.263才 (13.711–13.754)

13.576 ± 1.181 (13.558–13.594)

13.211 ± 1.013 (13.069–13.353)

(− 0.7889)(− 1.0887,-0.4892)

<0.0001

 Lisu

14.119 ± 1.274 (13.809–14.430)

14.224 ± 1.521 (14.153–14.296)

14.158 ± 1.409 (14.130–14.186)

13.971 ± 1.313 (13.948–13.993)

13.532 ± 0.958 (13.395–13.669)

(− 0.5878)(− 0.8812,-0.2944)

0.0001

 Hui

13.885 ± 1.451 (13.298–14.471)

13.583 ± 1.169 (13.506–13.661)

13.456 ± 1.117 (13.427–13.486)

13.353 ± 1.080 (13.331–13.376)

13.000 ± 0.977 (12.706–13.294)

(− 0.8846)(− 1.4602,-0.309)

0.0031

 Laku

14.000 ± 1.291(13.570–14.430)

13.968 ± 1.280 (13.887–14.050)

13.824 ± 1.237 (13.792–13.857)

13.616 ± 1.186 (13.588–13.644)

13.179 ± 1.111 (12.976–13.383)

(−0.8205)(−1.2514,-0.3896)

0.0002

 Wa

13.692 ± 1.104c (13.334–14.050)

13.720 ± 1.041 (13.658–13.783)

13.651 ± 1.090 (13.623–13.679)

13.595 ± 1.127 (13.565–13.624)

12.979 ± 1.053 (12.670–13.288)

(−0.7136)(−1.1771,-0.25)

0.003

 The others^b

14.213 ± 1.473 (13.874–14.552)

14.085 ± 1.394c (14.036–14.135)

13.929 ± 1.333 (13.910–13.949)

13.770 ± 1.257 (13.752–13.789)

13.389 ± 1.024c (13.252–13.526)

(−0.8244)(−1.1293,-0.5196)

<0.0001

 Rural

14.141 ± 1.404 (14.092–14.191)

13.884 ± 1.286 (13.876–13.892)

13.767 ± 1.234 (13.763–13.770)

13.619 ± 1.169 (13.616–13.622)

13.296 ± 1.038c (13.267–13.325)

(−0.845)(− 0.8984,-0.7917)

<0.0001

 urban

13.841 ± 1.391 (13.669–14.014)

13.621 ± 1.215 (13.594–13.649)

13.488 ± 1.175 (13.473–13.503)

13.361 ± 1.154 (13.341–13.382)

13.154 ± 1.14 4(12.463–13.845)

(−0.6874)(−1.4606,0.0858)

0.0812

 Extreme poverty

14.155 ± 1.327c (14.072–14.238)

14.008 ± 1.259 (13.993–14.023)

13.870 ± 1.163 (13.864–13.876)

13.712 ± 1.196 (13.706–13.717)

13.391 ± 1.034 (13.346–13.435)

(−0.7645)(− 0.8507,-0.6783)

<0.0001

 Middling poverty

14.178 ± 1.456 (14.103–14.252)

13.906 ± 1.316c (13.894–13.918)

13.784 ± 1.252 (13.779–13.789)

13.605 ± 1.190 (13.600–13.610)

13.215 ± 1.023 (13.174–13.256)

(−0.9627)(−1.0416,-0.8837)

<0.0001

 Non-poverty

13.990 ± 1.398 (13.901–14.080)

13.711 ± 1.240 (13.698–13.724)

13.631 ± 1.247 (13.626–13.637)

13.519 ± 1.205c (13.513–13.525)

13.285 ± 1.092c (13.195–13.376)

(−0.7052)(− 0.8405,-0.57)

<0.0001