Methods The persons aged 40 years and over in Zunyi,were investigated by the method of stratified cluster sampling , 1:1 case control study was used to analysis the risk factors.

• 方法 采用分层整群抽样方法 ,对遵义市部份 4 0a及以上的中老年进行流行病学调查 ,危险因素采用 1:1病例对照研究。