title: Bias.
abstract: The concept of bias is the lack of internal validity or incorrect assessment of the association between an exposure and an effect in the target population in which the statistic estimated has an expectation that does not equal the true value. Biases can be classified by the research stage in which they occur or by the direction of change in a estimate. The most important biases are those produced in the definition and selection of the study population, data collection, and the association between different determinants of an effect in the population. A definition of the most common biases occurring in these stages is given.
authors.affiliation: Division of Preventive Medicine and Public Health, University of Jaen, Spain. mdelgado@ujaen.es
authors.forename: Miguel
authors.initials: M
authors.lastname: Delgado-Rodríguez
authors.forename: Javier
authors.initials: J
authors.lastname: Llorca
mesh_terms: D015982:Bias; D015986:Confounding Factors, Epidemiologic; D003625:Data Collection / Q000379:methods* / Q000592:standards; D004812:Epidemiologic Methods; D006801:Humans; D015203:Reproducibility of Results; D012107:Research Design / Q000592:standards*; D015983:Selection Bias; D009626:Terminology as Topic