title: The control principle in scientific research.
abstract: The control principle is one of the four basic principles of research design. Without a control group, the conclusion of research will be unconvincing; furthermore, if the control group is not set properly, the conclusion will be unreliable. Generally, there is more than one control group in a multi-factor design. Problems like incomplete control and excessive control should be avoided. This article introduces the meaning and function of the control principle, common forms of control, common errors that researchers tend to make as well as analysis and differentiation of these errors.
authors.affiliation: Consulting Center of Biomedical Statistics, Academy of Military Medical Sciences, Beijing 100850, China. lphu812@sina.com
authors.forename: Liang-ping
authors.initials: LP
authors.lastname: Hu
authors.forename: Xiao-lei
authors.initials: XL
authors.lastname: Bao
authors.forename: Qi
authors.initials: Q
authors.lastname: Wang
mesh_terms: D018849:Controlled Clinical Trials as Topic; D006801:Humans; D012107:Research Design