Independent variables

With reference to previous research [23–26], seven categories of factors, which may be related to the prevalence of hypertension were used in this study. Firstly, demographic characteristics and health statuses, including seven variables: gender, age, height, weight, educational achievement, marital status and self-reported diabetes status. BMI was calculated as weight divided by the square of the height (kg/m²). BMI were categorized as underweight (BMI < 18.5 kg/m²), normal weight (18.5 ≤ BMI < 25.0 kg/m²), overweight (25.0 ≤ BMI < 30.0 kg/m²) and obese (BMI ≥ 30.0 kg/m²) according to WHO classifications [3, 27]. The interviewees were asked: “Have you ever been diagnosed with diabetes by a doctor?” A subject was defined as having diabetes if he/she answered “Yes”. Secondly, utilization of preventative health service, including a dummy variable (e.g. whether receive preventative health service during the last 4 weeks). Thirdly, basic health insurance, including a dummy variable: having basic health insurance or not. Fourthly, economic status was measured by annual individual income, and grouped into five quintiles. Furthermore, geographic characteristic (area), consisting of 9 provinces including Liaoning, Heilongjiang, Jiangsu, Shandong, Henan, Hubei, Hunan, Guangxi and Guizhou, which were grouped into three areas (e.g. East, Middle and West of China). Finally, risk factors for hypertension, including two variables: smoking and drinking. Specially, respondents who ever consumed any form of tobacco were defined as smokers; respondents who consumed beer or any other alcoholic beverage last year were defined as drinkers. With reference to previous research, only variables passed the multicollinearity test were included, with none of the variables having a VIF greater than 4 [28].