title: Hypothetical interventions to limit metalworking fluid exposures and their effects on COPD mortality: G-estimation within a public health framework.
abstract: BACKGROUND
  Current recommendations for limits on metalworking fluids may provide insufficient protection from workplace-related illness. Chronic obstructive pulmonary disease (COPD) is a challenging outcome in occupational cohorts because its long period of worsening pulmonary function allows sicker workers to reduce exposure, causing a healthy worker survivor bias. G-estimation is a statistical method that reduces this bias. We introduce a public health approach using g-estimation to compare a series of potential exposure-reducing interventions.
  
  
  METHODS
  Autoworkers at three General Motors plants in Michigan were followed for COPD mortality from 1 January 1941 to 31 December 1994. For each of the three fluid types (straight, soluble, synthetic), a series of binary variables indicated whether exposure exceeded a series of potential limits. Separate g-estimation analyses for each limit yielded results expressed as the total number of years of life that could have been saved among those who died from COPD had that exposure limit been enforced.
  
  
  RESULTS
  Lower limits would have had greater effect than higher limits. A ban on soluble fluids (the most common type) would have had the greatest effect, saving an estimated 1550 years of life. Corresponding estimates were 737 and 260 years for straight and synthetic fluids, respectively. Few workers were exposed to synthetic fluids, limiting analytic power.
  
  
  CONCLUSIONS
  This application of g-estimation suggests that limiting exposure to metalworking fluids could have saved many years of life lost to COPD in this cohort. The approach permits comparison of different interventions. Separate limits should be considered for different types of fluids.
authors.affiliation: From the aUniversity of California, Berkeley, School of Public Health, Environmental Health Sciences, Berkeley, CA; bUniversity of California, Berkeley, School of Public Health, Epidemiology, Berkeley, CA; and cUniversity of California, San Francisco, School of Medicine, Occupational and Environmental Medicine, San Francisco, CA.
authors.forename: Sally
authors.initials: S
authors.lastname: Picciotto
authors.forename: Jonathan
authors.initials: J
authors.lastname: Chevrier
authors.forename: John
authors.initials: J
authors.lastname: Balmes
authors.forename: Ellen A
authors.initials: EA
authors.lastname: Eisen
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001336:Automobiles; D015331:Cohort Studies; D005260:Female; D006801:Humans; D015994:Incidence; D007219:Industrial Oils / Q000009:adverse effects*; D008297:Male; D008669:Metallurgy; D008875:Middle Aged; D015233:Models, Statistical; D009784:Occupational Diseases / Q000139:chemically induced / Q000401:mortality*; D016273:Occupational Exposure / Q000009:adverse effects* / Q000517:prevention & control*; D016272:Occupational Health; D011634:Public Health / Q000592:standards; D029424:Pulmonary Disease, Chronic Obstructive / Q000139:chemically induced / Q000401:mortality*; D012189:Retrospective Studies; D015996:Survival Rate; D013997:Time Factors; D014481:United States