Figure 1From: Population-based study on the prevalence of and risk factors for human papillomavirus infection in Qujing of Yunnan province, Southwest ChinaStrategy of sampling.†Qilin central city zone, Xuanwei city, and 7 counties. * The town where the local government of the county located. # Individuals were drawn up with simple random sampling method. 9 age strata with PPS were defined in order to maintain a large enough sample size for statistical power.Back to article page