The impact of work environment, utility, and sampling design on occupational magnetic field exposure summaries

Most recent epidemiologic studies investigating the potential health effect s of occupational magnetic field (MF) exposure have relied on MF measuremen t data linked to job titles. These measurements are summarized by occupatio nal categories, which represent similar groups of job titles. However, job titles alone explain only a small proportion of exposure variability. A com prehensive MF occupational exposure database was used to (1) develop summar y job-specific estimates of magnetic field exposure, (2) evaluate the impac t of incorporating work environment data to improve electric and magnetic f ield exposure assessment, and (3) evaluate the use of random versus nonrand om sampling when estimating mean MF exposure levels by occupational categor ies. Uniform classification systems were developed for occupational and wor k environment data. A factorial design was used to summarize and calculate arithmetic means and 95% confidence intervals for occupational MF data, ass uming that the total variation in MF exposure resulted from variation in oc cupation, work environment, utility worker, and day. Occupation-specific me ans varied across different work environments, particularly for craft worke rs, Although within-worker and between-worker variability account for a lar ge proportion (over 50%) of exposure variation, work environment (24%) acco unted for more exposure variability than occupation (4.9%) or utility (15%) . Some differences were observed when results were compared from surveys th at used random and nonrandom sampling; however, these differences were not consistent or systematic. It was concluded that MF exposure assessment shou ld consider work environment in addition to job title to reduce exposure mi sclassification.