title: Regression dilution bias: tools for correction methods and sample size calculation.
abstract: BACKGROUND
  Random errors in measurement of a risk factor will introduce downward bias of an estimated association to a disease or a disease marker. This phenomenon is called regression dilution bias. A bias correction may be made with data from a validity study or a reliability study.
  
  
  OBJECTIVE
  In this article we give a non-technical description of designs of reliability studies with emphasis on selection of individuals for a repeated measurement, assumptions of measurement error models, and correction methods for the slope in a simple linear regression model where the dependent variable is a continuous variable. Also, we describe situations where correction for regression dilution bias is not appropriate.
  
  
  RESULTS
  The methods are illustrated with the association between insulin sensitivity measured with the euglycaemic insulin clamp technique and fasting insulin, where measurement of the latter variable carries noticeable random error. We provide software tools for estimation of a corrected slope in a simple linear regression model assuming data for a continuous dependent variable and a continuous risk factor from a main study and an additional measurement of the risk factor in a reliability study. Also, we supply programs for estimation of the number of individuals needed in the reliability study and for choice of its design.
  
  
  CONCLUSIONS
  Our conclusion is that correction for regression dilution bias is seldom applied in epidemiological studies. This may cause important effects of risk factors with large measurement errors to be neglected.
authors.affiliation: Uppsala Clinical Research Center (UCR), Uppsala University Hospital, Sweden. lars.berglund@ucr.uu.se
authors.forename: Lars
authors.initials: L
authors.lastname: Berglund
mesh_terms: D015233:Models, Statistical; D012044:Regression Analysis; D015203:Reproducibility of Results; D012307:Risk Factors; D018401:Sample Size