title: The impact of imprecisely measured covariates on estimating gene-environment interactions.
abstract: BACKGROUND
  The effects of measurement error in epidemiological exposures and confounders on estimated effects of exposure are well described, but the effects on estimates for gene-environment interactions has received rather less attention. In particular, the effects of confounder measurement error on gene-environment interactions are unknown.
  
  
  METHODS
  We investigate these effects using simulated data and illustrate our results with a practical example in nutrition epidemiology.
  
  
  RESULTS
  We show that the interaction regression coefficient is unchanged by confounder measurement error under certain conditions, but biased by exposure measurement error. We also confirm that confounder measurement error can lead to estimated effects of exposure biased either towards or away from the null, depending on the correlation structure, with associated effects on type II errors.
  
  
  CONCLUSIONS
  Whilst measurement error in confounders does not lead to bias in interaction coefficients, it may still lead to bias in the estimated effects of exposure. There may still be cost implications for epidemiological studies that need to calibrate all error-prone covariates against a valid reference, in addition to the exposure, to reduce the effects of confounder measurement error.
authors: Biostatistics Unit, University of Leeds, Leeds, UK. d.c.greenwood@leeds.ac.uk
authors: Darren C
authors: DC
authors: Greenwood
authors: Mark S
authors: MS
authors: Gilthorpe
authors: Janet E
authors: JE
authors: Cade