title: Assessment of exposure to shiftwork mechanisms in the general population: the development of a new job-exposure matrix.
abstract: OBJECTIVE
  To develop a job-exposure matrix (JEM) that estimates exposure to eight variables representing different aspects of shiftwork among female workers.
  
  
  METHODS
  Occupational history and shiftwork exposure data were obtained from a population-based breast cancer case-control study. Exposure to light at night, phase shift, sleep disturbances, poor diet, lack of physical activity, lack of vitamin D, and graveyard and early morning shifts, was calculated by occupational code. Three threshold values based on the frequency of exposure were considered (10%, 30% and 50%) for use as cut-offs in determining exposure for each occupational code. JEM-based exposure classification was compared with that from the OccIDEAS application (job-specific questionnaires and assessment by rules) by assessing the effect on the OR for phase shift and breast cancer. Using data from the Australian Workplace Exposure Study, the specificity and sensitivity of the threshold values were calculated for each exposure variable.
  
  
  RESULTS
  127 of 413 occupational codes involved exposure to one or more shiftwork variables. Occupations with the highest probability of exposure shiftwork included nurses and midwives. Using the 30% threshold, the OR for the association between phase shift exposure and breast cancer was decreased and no longer statistically significant (OR=1.14, 95% CI 0.92 to 1.42). The 30% cut-off point demonstrated best specificity and sensitivity, although results varied between exposure variables.
  
  
  CONCLUSIONS
  This JEM provides a set of indicators reflecting biologically plausible mechanisms for the potential impact of shiftwork on health and may provide an alternative method of exposure assessment in the absence of detailed job history and exposure data.
authors.affiliation: Discipline of Obstetrics and Gynaecology, University of Adelaide, Adelaide, South Australia, Australia Discipline of Public Health, University of Adelaide, Adelaide, South Australia, Australia.
authors.forename: Renae C
authors.initials: RC
authors.lastname: Fernandez
authors.affiliation: Occupational Respiratory Epidemiology, School of Population Health, The University of Western Australia, Perth, Western Australia, Australia.
authors.forename: Susan
authors.initials: S
authors.lastname: Peters
authors.affiliation: School of Public Health, Curtin University, Perth, Western Australia, Australia.
authors.forename: Renee N
authors.initials: RN
authors.lastname: Carey
authors.affiliation: Discipline of Obstetrics and Gynaecology, University of Adelaide, Adelaide, South Australia, Australia Robinson Research Institute, University of Adelaide, Adelaide, South Australia, Australia.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Davies
authors.affiliation: School of Public Health, Curtin University, Perth, Western Australia, Australia.
authors.forename: Lin
authors.initials: L
authors.lastname: Fritschi
mesh_terms: D001943:Breast Neoplasms / Q000453:epidemiology*; D005260:Female; D006801:Humans; D008019:Life Style; D016273:Occupational Exposure / Q000706:statistics & numerical data; D009790:Occupations / Q000145:classification; D010561:Personnel Staffing and Scheduling; D018570:Risk Assessment; D012680:Sensitivity and Specificity