title: Study design II. Issues of chance, bias, confounding and contamination.
abstract: In the first article in the series I explained the importance of study design and gave an overview of the main types of design. Here, I describe the ways in which the results of a study may deviate from the truth and the measures that can be taken to help minimise this when designing a study.
authors.affiliation: Dental Health Services Research Unit, Dundee, Scotland, UK.
authors.forename: Kate Ann
authors.initials: KA
authors.lastname: Levin
mesh_terms: D015982:Bias; D018592:Cross-Over Studies; D006801:Humans; D015588:Observer Variation; D018579:Patient Selection; D011897:Random Allocation; D012107:Research Design; D015983:Selection Bias