Characteristics of participants by migration status and period, Yi migrant study, 1996–2015
| Variable | Farmers | Migrants | ||||||
| 1996 n=723 | 2007 n=2351 | 2015 n=1966 | P for trend | 1996 n=679 | 2007 n=1393 | 2015 n=1336 | P for trend | |
| Mean age, years (SD) | 35.0 (12.7) | 39.4 (12.0) | 45.3 (12.8) | <0.0001* | 37.9 (11.2) | 39.6 (12.0) | 48.3 (14.4) | <0.0001* |
| Mean BMI, kg/m2 (SD) | 20.3 (2.1) | 21.4 (2.6) | 22.3 (3.6) | <0.0001† | 22.4 (3.0) | 23.5 (3.7) | 24.4 (3.8) | <0.0001† |
| Male, % (N) | 63.5 (459) | 47.1 (1107) | 33.8 (664) | <0.0001‡ | 57.1 (388) | 57.3 (798) | 33.1 (442) | <0.0001‡ |
| BMI categories, % (N)§ | <0.0001¶ | <0.0001¶ | ||||||
| Underweight (BMI <18.5) | 15.3 (110) | 9.4 (220) | 12.8 (249) | 8.3 (56) | 7.2 (100) | 5.0 (66) | ||
| Normal weight (BMI 18.5–23.9) | 81.8 (588) | 78.4 (1837) | 58.3 (1133) | 63.4 (428) | 51.6 (718) | 42.3 (560) | ||
| Overweight (BMI 24–27.9) | 2.5 (18) | 10.6 (248) | 21.8 (423) | 23.7 (160) | 30.1 (418) | 35.4 (468) | ||
| Obesity (BMI ≥28) | 0.4 (3) | 1.7 (39) | 7.1 (138) | 4.6 (31) | 11.1 (155) | 17.4 (230) | ||
| Education, % (N)§ | <0.0001¶ | <0.0001¶ | ||||||
| Low | 92.3 (658) | 91.5 (2109) | 88.4 (1738) | 19.2 (130) | 24.2 (329) | 49.3 (658) | ||
| Middle | 7.0 (50) | 7.6 (175) | 10.4 (204) | 62.3 (421) | 38.6 (524) | 32.4 (432) | ||
| High | 0.7 (5) | 0.9 (21) | 1.2 (24) | 18.5 (125) | 37.1 (504) | 18.4 (245) | ||
| Hypertension, % (N) | 3.5 (25) | 5.5 (130) | 13.0 (255) | <0.0001** | 8.0 (54) | 14.8 (206) | 23.7 (316) | <0.0001** |
*P values were calculated by simple linear regression model in which age was the dependent variable and period was the independent variable.
†P values were calculated by multiple linear regression model in which BMI was the dependent variable and age, sex and period were independent variables.
‡P values were calculated by Cochran-Armitage trend test.
§Numbers do not sum up to the total due to missing data.
¶P values were calculated by cumulative logistic model in which BMI categories or education was the dependent variable and age, sex and period were independent variables.
**P values were calculated by binary logistic regression model in which hypertension was the dependent variable and age, sex and period were independent variables.
BMI, body mass index.