title: Bias: adding to the uncertainty.
authors.forename: J M
authors.initials: JM
authors.lastname: Sparrow
authors.forename: J R
authors.initials: JR
authors.lastname: Thompson
mesh_terms: D015982:Bias; D015986:Confounding Factors, Epidemiologic; D005124:Eye Abnormalities / Q000453:epidemiology; D006801:Humans; D016032:Randomized Controlled Trials as Topic; D012107:Research Design; D015983:Selection Bias