[The protocol and design of etiological study.].
An accurate diagnosis and effective treatment are based on deep insight into the etiology of a disease. With the development of society, some diseases have been controlled successfully since their cause and mechanism are well understood, but a few more new diseases arose. It is necessary to study them by a proper design for establishing a correct diagnosis and effective therapy. The basic knowledge is rather important for clinicians. This paper introduces the commonly used protocol and design of etiological study with an example of the study on caries etiology.