title: Modelling complex mixtures in epidemiologic analysis: additive versus relative measures for differential effectiveness.
abstract: OBJECTIVE
  Mixed exposures are often combined into single exposure measures using weighting factors. This occurs for many complex mixtures in environmental and occupational epidemiology including multiple congeners, air pollutants and unique forms of ionising radiation, among others.
  
  
  METHODS
  The weights used for combining exposures are most often determined from experimental animal and cellular research. However, evidence from observational research is necessary to support their use in risk analyses, since results from experimental research do not directly translate to observational epidemiology.
  
  
  RESULTS
  Using simulated data, we show that ratio-based relative weights cannot be reliably estimated from observational research. As a solution to this problem, we propose an approach for estimating differences in effectiveness of distinct exposures based on their excess effectiveness compared with a reference exposure.
  
  
  CONCLUSIONS
  This alternative is easy to calculate and provides reliable estimates of differences in effectiveness of distinct exposures. This is important to regulatory bodies using relative measures for policy decisions, as well as practicing epidemiologists conducting risk analyses.
authors.affiliation: Section of Environment and Radiation, International Agency for Research on Cancer, Lyon, France.
authors.forename: Ghassan Badri
authors.initials: GB
authors.lastname: Hamra
authors.forename: Richard
authors.initials: R
authors.lastname: MacLehose
authors.forename: David
authors.initials: D
authors.lastname: Richardson
authors.forename: Stephen
authors.initials: S
authors.lastname: Bertke
authors.forename: Robert D
authors.initials: RD
authors.lastname: Daniels
mesh_terms: D045424:Complex Mixtures / Q000633:toxicity*; D004781:Environmental Exposure; D004812:Epidemiologic Methods; D006801:Humans; D008962:Models, Theoretical; D016273:Occupational Exposure
chemical_list: D045424:Complex Mixtures