Table 3 Univariate Cox proportional hazard model of age at menarche

Bodyweight (kg)

1.013 (1.008–1.017)

<.0001

Height (cm)

1.003 (0.996–1.010)

.4293

Maternal age at menarche (y)

 Younger (<13.0)

1.514 (1.256–1.826)

<.0001

 Normal (13.0–15.9)

1.00

 Older (≥16.0)

0.707 (0.622–0.804)

<.0001

BMI (kg/m²)

 Underweight

0.327 (0.193–0.554)

<.0001

 Normal

1.00

 Overweight

1.227 (1.076–1.400)

.0023

 Obese

1.258 (1.058–1.495)

.0093

Household income

 Low

1.00

 Lower middle

1.117 (0.978–1.276)

.1030

 Upper middle

1.159 (1.018–1.320)

.0259

 High

1.207 (1.059–1.378)

.0047

Paternal education level

 No schooling

1.00

 Elementary school

1.188 (0.571–2.474)

.6446

 Middle school

0.997 (0.487–2.040)

.9924

 High school

1.266 (0.628–2.552)

.5093

 College or university

1.463 (0.752–2.950)

.2880

Maternal education level

 No schooling

1.00

 Elementary school

0.974 (0.504–1.880)

.9363

 Middle school

0.895 (0.471–1.701)

.7351

 High school

1.096 (0.585–2.053)

.7740

 College or university

1.370 (0.729–2.577)

.3280

Place of residence

 Rural

1.00

 Urban

1.039 (0.954–1.131)

.3804