Impact of aggregating exposure information from cases and controls when building a population-based job-exposure matrix from past expert evaluations

Development of a Job-Exposure Matrix for Assessment of Occupational Exposure to High-Frequency Electromagnetic Fields (3 kHz-300 GHz)

OBJECTIVES

The aim of this work was to build a job-exposure matrix (JEM) using an international coding system and covering the non-thermal intermediate frequency (IF) (3-100 kHz, named IFELF), thermal IF (100 kHz-10 MHz, named IFRF), and radiofrequency (RF) (>10 MHz) bands.

METHODS

Detailed occupational data were collected in a large population-based case-control study, INTEROCC, with occupations coded into the International Standard Classification of Occupations system 1988 (ISCO88). The subjects' occupational source-based ancillary information was combined with an existing source-exposure matrix and the reference levels of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) for occupational exposure to calculate estimates of level (L) of exposure to electric (E) and magnetic (H) fields by ISCO88 code and frequency band as ICNIRP ratios (IFELF) or squared ratios (IFRF and RF). Estimates of exposure probability (P) were obtained by dividing the number of exposed subjects by the total number of subjects available per job title.

RESULTS

With 36 011 job histories collected, 468 ISCO88 (four-digit) codes were included in the JEM, of which 62.4% are exposed to RF, IFRF, and/or IFELF. As a reference, P values for RF E-fields ranged from 0.3 to 65.0% with a median of 5.1%. L values for RF E-fields (ICNIRP squared ratio) ranged from 6.94 × 10-11 to 33.97 with a median of 0.61.

CONCLUSIONS

The methodology used allowed the development of a JEM for high-frequency electromagnetic fields containing exposure estimates for the largest number of occupations to date. Although the validity of this JEM is limited by the small number of available observations for some codes, this JEM may be useful for epidemiological studies and occupational health management programs assessing high-frequency electromagnetic field exposure in occupational settings.

Development of a Coding and Crosswalk Tool for Occupations and Industries

Introduction

Job coding into a standard occupation or industry classification is commonly performed in occupational epidemiology and occupational health. Sometimes, it is necessary to code jobs into multiple classifications or to convert job codes from one classification to another. We developed a generic tool, called CAPS-Canada (http://www.caps-canada.ca/), that combines a computer-assisted coding tool covering seven International, Canadian and US occupation and industry classifications and an assistant facilitating crosswalks from one classification to another. The objectives of this paper are to present the different functions of the CAPS-Canada tool and to assess their contribution through an inter-rater reliability study.

Method

The crosswalk assistant was built based on a database of >30,000 jobs coded during a previous project. We evaluated to what extent it would allow automatic translation between pairs of classifications. The influence of CAPS-Canada on agreement between coders was assessed through an inter-rater reliability study comparing three approaches: manual coding, coding with CAPS-Canada without the crosswalk assistant, and coding with the complete tool. The material for this trial consisted of a random sample of 1000 jobs extracted from a case-control study and divided into three subgroups of equivalent size.

Results

Across the classification systems, the crosswalk assistant would provide useful information for 83-99% of jobs (median 95%) in a population similar to ours. Eighteen to eighty-one percent of jobs (median 56%) could be entirely automatically recoded. Based on our sample of 1000 jobs, inter-rater reliability in occupation coding ranged from 35.7 to 66.5% (median 53.7%) depending on the combination of classification/resolution. Compared with manual coding, the use of CAPS-Canada substantially improved inter-rater reliability.

Conclusion

CAPS-Canada is an attractive alternative to manual coding and is particularly relevant for coding a job into multiple classifications or for recoding jobs into other classifications.

Agreement in Occupational Exposures Between Men and Women Using Retrospective Assessments by Expert Coders

Objectives

To estimate the level of agreement and identify notable differences in occupational exposures (agents) between men and women from retrospective assessments by expert coders.

Methods

Lifetime occupational histories of 1657 men and 2073 women from two case-control studies, were translated into exposure estimates to 243 agents, from data on 13882 jobs. Exposure estimates were summarized as proportions and frequency-weighted intensity of exposure for 59 occupational codes by sex. Agreement between metrics of exposure in men's and women's jobs was determined with intraclass correlation coefficients (ICC) and weighted Kappa coefficients, using as unit of analysis ('cell') a combination of occupational code and occupational agent. 'Notable' differences between men and women were identified for each cell, according to a Bayesian hierarchical model for both proportion and frequency-weighted intensity of exposure.

Results

For cells common to both men and women, the ICC for continuous probability of exposure was 0.84 (95% CI: 0.83-0.84) and 7.4% of cells showed notable differences with jobs held by men being more often exposed. A weighted kappa of 0.67 (95% CI: 0.61-0.73) was calculated for intensity of exposure, and an ICC of 0.67 (95% CI: 0.62-0.71) for frequency-weighted intensity of exposure, with a tendency of higher values of exposure metrics in jobs held by men.

Conclusions

Exposures were generally in agreement between men and women. Some notable differences were identified, most of them explained by differential sub-occupations or industries or dissimilar reported tasks within the studied occupations.

Development of and Selected Performance Characteristics of CANJEM, a General Population Job-Exposure Matrix Based on Past Expert Assessments of Exposure

Objectives

We developed a job-exposure matrix called CANJEM using data generated in population-based case-control studies of cancer. This article describes some of the decisions in developing CANJEM, and some of its performance characteristics.

Methods

CANJEM is built from exposure information from 31673 jobs held by study subjects included in our past case-control studies. For each job, experts had evaluated the intensity, frequency, and likelihood of exposure to a predefined list of agents based on jobs histories and descriptions of tasks and workplaces. The creation of CANJEM involved a host of decisions regarding the structure of CANJEM, and operational decisions regarding which parameters to present. The goal was to produce an instrument that would provide great flexibility to the user. In addition to describing these decisions, we conducted analyses to assess how well CANJEM covered the range of occupations found in Canada.

Results

Even at quite a high level of resolution of the occupation classifications and time periods, over 90% of the recent Canadian working population would be covered by CANJEM. Prevalence of exposure of specific agents in specific occupations ranges from 0% to nearly 100%, thereby providing the user with basic information to discriminate exposed from unexposed workers. Furthermore, among exposed workers there is information that can be used to discriminate those with high exposure from those with low exposure.

Conclusions

CANJEM provides good coverage of the Canadian working population and possibly that of several other countries. Available in several occupation classification systems and including 258 agents, CANJEM can be used to support exposure assessment efforts in epidemiology and prevention of occupational diseases.