title: A graphical tool to evaluate temporal coverage of occupational history by exposure measurements.
abstract: BACKGROUND
  In occupational epidemiology, differences in the temporal coverage of the exposure history by available exposure measurement data may affect the uncertainty of exposure estimates. In the reporting of results of studies, greater attention should be paid to the extent to which exposure assessments require extrapolation outside the timeframe for which exposure measurements are available. We propose a simple graphical method that can be used to visualise the temporal coverage of exposure history with exposure measurements and the extent of temporal extrapolation needed.
  
  
  METHODS
  We construct a graph that displays the accumulated work history years for which exposure had to be assessed in each calendar year. Years for which exposure measurements were available are shaded. The proportion of work history years covered by exposure measurements and the proportion of work history years accrued before the first measurements are summarised. When available, the actual number of measurements available in each calendar year is shown.
  
  
  RESULTS
  We demonstrate the application of the graphical tool in three nested case-control studies that reported on leukaemia in relation to low-level benzene exposures in the petroleum industry. Considerable differences in temporal coverage between the studies were illustrated, which may have resulted in differences in the reliability of the retrospective exposure estimates derived for these studies.
  
  
  CONCLUSIONS
  We introduce a graphical tool for visualising the temporal coverage by available exposure measurement data in epidemiological studies and encourage others to use similar graphs to derive and share better qualitative insights into the uncertainty in exposure assessment.
authors.affiliation: Institute for Risk Assessment Sciences, Division Environmental Epidemiology, Utrecht University, 3508 TD, Utrecht, The Netherlands. j.j.vlaanderen@uu.nl
authors.forename: Jelle
authors.initials: J
authors.lastname: Vlaanderen
authors.forename: Wouter
authors.initials: W
authors.lastname: Fransman
authors.forename: Brian
authors.initials: B
authors.lastname: Miller
authors.forename: Igor
authors.initials: I
authors.lastname: Burstyn
authors.forename: Dick
authors.initials: D
authors.lastname: Heederik
authors.forename: Fintan
authors.initials: F
authors.lastname: Hurley
authors.forename: Roel
authors.initials: R
authors.lastname: Vermeulen
authors.forename: Hans
authors.initials: H
authors.lastname: Kromhout
mesh_terms: D001315:Australia / Q000453:epidemiology; D001554:Benzene / Q000032:analysis / Q000633:toxicity; D002170:Canada / Q000453:epidemiology; D016022:Case-Control Studies; D003196:Computer Graphics; D004651:Employment / Q000706:statistics & numerical data; D006801:Humans; D007938:Leukemia / Q000139:chemically induced / Q000453:epidemiology; D009784:Occupational Diseases / Q000453:epidemiology / Q000209:etiology*; D016273:Occupational Exposure / Q000009:adverse effects / Q000032:analysis*; D010578:Petroleum; D006113:United Kingdom / Q000453:epidemiology
chemical_list: D010578:Petroleum; D001554:Benzene