病因问题是一切医疗实践活动 (诊断、治疗及预防 )的重要理论基础 ,因此它在医学研究领域中始终占有重要地位。多年来 ,流行病学从群体的角度出发对病因问题提出了许多独到的见解 ,并对许多疾病的病因在新的层次上进行了阐释[1] 。然而 ,发展总是与问题并存。当前 ,流行病学在 The etiology problem is an important theoretical basis for all medical practice activities (diagnosis, treatment and prevention), and therefore it always occupies an important position in the field of medical research. Over the years, epidemiology has provided many unique insights into etiology from a group point of view and has elucidated the etiology of many diseases at a new level [1]. However, development always coexists with problems. At present, epidemiology is