What methods are available for assessing occupation?

 

 

It has long been a challenge for epidemiologists to come up with a method for occupational exposure assessment that minimizes misclassification, entails transparent assessment processes, removes the need for repetitive tasks, and produces consistent, repeatable results.

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Traditionally, occupational studies have been industry-based cohort studies.  The research team usually have access to many years worth of monitoring data and this can be used to reconstruct exposure histories for workers in those factories. This is considered the “gold standard” in occupational assessment.  

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Obtaining monitoring data within community-based studies such as case-control studies or population-based cohort studies is more difficult.  Subjects are employed over a wide range of occupations and employers and the majority of workers today work in small to medium sized enterprises which usually do not have the capability to regularly measure and record chemical exposure levels.

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There are several more indirect ways of assessing occupational exposure – job titles, self-report, job exposure matrices, and expert assessment.

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Job titles are accurately reported by subjects, but a job title alone does not give any indication of what agent might be relevant in disease causation.  In addition, there are often too few subjects in each job title for analysis.  On the other hand, if you combine many job titles, the resulting category is very broad and the variation of exposure within each category will lead to misclassification.

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Self-report involves asking subjects whether they have been exposed to a list of agents.  However, workers are not always aware of the chemicals which are used in their workplace and have difficulty in assessing their level of exposure as compared with levels of exposure in other workplaces.  There is also a risk of recall bias in retrospective studies.
Job exposure matrices consist of a matrix with job titles on one axis and agents on the other axis. The value in each cell indicates whether that job is exposed to that agent.  Job exposure matrices can be developed based on databases of monitoring data, or by panels of experts.  The main drawback of using job exposure matrices is that the same exposure is assigned to all workers in the same job title.  Many job titles have wide variability in the work undertaken (such as janitors, nurses, or assembly workers). This means that there will be misclassification of exposure status for these jobs with everyone assigned the same exposure whether or not they do the relevant tasks which involve exposure.

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In the expert assessment method, a full job history is provided by the subjects.  The subjects are then asked questions from job-specific modules (modules) which are questionnaires containing questions regarding tasks within a particular job (e.g., farmer, driver, plumber).  An expert reviews the answers to the questions and assigns exposures.  Because the expert can use their own experience, as well as literature and other exposure databases, this avoids the problems of self-report.  Because the expert assesses each job individually it avoids the problems of job exposure matrices.  However, the expert assessment process is very labour intensive and costly and requires access to highly trained experts for long periods of time.  In addition, it is not obvious how each assessment decision was arrived at.

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OccIDEAS uses the best aspects of all these methods and combines them with the power of modern computing.  Using OccIDEAS, the first step is to obtain a job history from the subjects, and then OccIDEAS is used to assign a module to each job.  The module can either be administered by interview, or can be completed on-line.  The questions within the modules are focussed on the established determinants of exposure and have been developed using the combined expertise of a team of experienced occupational hygienists and epidemiologists.  For example, the amount of wood dust a carpenter is exposed to might depend on whether s/he used power or hand tools, whether s/he worked indoors or outdoors, whether a dust extraction fan was present, and whether s/he wore a mask.  All these questions are easily answered by subjects.  Rules within OccIDEAS automatically assign exposure depending on the answers to these questions.

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OccIDEAS therefore provides the best option for those who want to assess occupation in epidemiological studies.  It gives you access to an assessment process which has been developed using a team of highly experienced occupational hygienists and epidemiologists.  It means you don’t need to learn all about the complications of various jobs, you tap into our expertise and get a high level assessment of these important exposures.

For more discussion on the types of occupational exposure assessment (other than OccIDEAS) see:

• Teschke K, Olshan AF, Daniels JL, De Roos AJ, Parks CG, Schulz M, Vaughan TL. Occupational exposure assessment in case-control studies: opportunities for improvement.  Occup Environ Med. 2002 Sep;59(9):575-93; discussion 594.

• McGuire V, Nelson LM, Koepsell TD, Checkoway H, Longstreth WT Jr. Assessment of occupational exposures in community-based case-control studies.   Annu Rev Public Health. 1998;19:35-53.

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