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Exposure matrices: how to create them, how to use them, and what they
can tell us
Dr Sean SempleDepartment of Environmental & Occupational Medicine
University of Aberdeen
Scotland
Overview
What are JEMs? Variability and uncertainty Industry specific and generic JEMs Coding by industry and occupation Creating a JEM Training people to use a JEM The Geoparkinson study How good are JEMs?
Job exposure matrix
Cross-tabulation of jobs and exposure agents
Each cell contains one or more indices of exposure
– Presence, intensity (variability), frequency and/or probability
Combine with job history data Allows estimation of exposure to
particular agents over a working lifetime
A simple ever/never JEM…
Industrial sector Job title Chemical group
Solvents Welding Fume Pesticides
Agriculture Farm Labourer yes yes yes
Farmer yes yes yes
Construction Welder no yes no
Painter yes no no
Lorry driver yes no no
Manufacturing Factory worker yes no no
Metal worker yes yes no
Wood worker yes no no
A quantitative JEM…
Industrial sector Job title Chemical group
Solvents Welding Fume Pesticides
Agriculture Farm Labourer 2 2 3
Farmer 1 1 2
Construction Welder 0 3 0
Painter 3 0 0
Lorry driver 1 0 0
Manufacturing Factory worker 2 0 0
Metal worker 1 2 0
Wood worker 1 0 0
0= no exposure; 1= low exposure; 2=medium exposure; 3= high exposure
A JEM with intensity and frequency…
Industrial sector Job title Chemical group
Solvents Welding Fume Pesticides
Agriculture Farm Labourer 2,1 2,1 3,3
Farmer 1,1 1,1 2,3
Construction Welder 0 3,3 0
Painter 3,3 0 0
Lorry driver 1,3 0 0
Manufacturing Factory worker 2,2 0 0
Metal worker 1,3 2,3 0
Wood worker 1,3 0 0
0= no exposure; 1= low exposure; 2=medium exposure; 3= high exposure
1= rare event; 2=sporadic event; 3= regular event
Additional layers
Time or era dimension– Processes change over time– Understanding of the hazards changes– Laws change
Facility or country layer– Different plants may produce the same product using
different techniques or using different control measures– Different legislative frameworks between countries
Tasks within each job– Task-exposure matrices
Uncertainty and variability
Uncertainty– How good is the data used to generate the
JEM– Is it based on measurements or estimates
Variability– Intra-worker, inter-worker
Probabilistic modelling– Select from distribution of exposures
Industry specific and generic JEMs
JEMs are particularly useful for industry-based cohorts
– can be based on available measurements from a particular plant, going back in time
Generic JEMs for population-based case-control studies usually based on some expert-system or assessment
– Gomez et al., 1994- chlorinated hydrocarbons; Kauppinen et al., 1998 Finnish JEM- all chemical, biological and physical stressors; Kennedy et al., 2000- asthmagens.
SOC
SOC 2000 Standard Occupational Classification– 9 major groups– 25 sub-major groups– 81 minor groups– 353 Unit groups
1 Managers and Senior Officials2 Professional Occupations3 Associate Professional and Technical Occupations4 Administrative and Secretarial Occupations5 Skilled Trades Occupations6 Personal Service Occupations7 Sales and Customer Service Occupations8 Process, Plant and Machine Operatives9 Elementary Occupations
SIC(92)
Standard Industrial Classification of Economic Activities
– 17 sections– 16 subsections– 60 divisions– 222 groups– 503 classes – 253 subclasses
A agriculture, hunting and forestryB fishingC mining and quarrying D manufacturingE electricity, gas and water supply F constructionG wholesale and retail trade; Repair of motor vehicles, motorcycles and personal and household goodsH hotels and restaurantsI transport, storage and communicationJ financial intermediationK real estate, renting and business activitiesL public administration and defence; Compulsory social securityM educationN health and social workO other community, social & personal service activitiesP private households with employed personsQ extra - territorial organisations and bodies
Cascot: Computer Assisted Structured Coding Tool
Cascot software program designed to make the coding of text information to standard classifications simpler, quicker and more reliable.
Capable of occupational coding and industrial coding to the UK standards developed by the UK Office for National Statistics. These are the Standard Occupational Classification (SOC) and the Standard Industrial Classification (SIC).
Quality of coding performed by Cascot depends on the quality of the input text.
Developed by Peter Elias at the University of Warwick http://www2.warwick.ac.uk/fac/soc/ier/publications/software/cascot/
Teaching others how to create JEMs Requires an understanding of the material or
chemicals being assessed Requires an understanding of the industry and
processes Make sure the detail of job and industry data
being gathered from the study population matches that of the JEM
Differences by country- local knowledge Differences over time- experience and
interviews with long-serving employees Consider all exposure routes- inhalation, dermal
and ingestion Is validation possible?
Examining a JEM for use How was it generated? Has it been validated?
– Measurements– Biomarkers of exposure
What is the source material?– JEM is only as good as the experts
who created it! Is it applicable to the population under
study?– A JEM created for the Finnish
population may not perform well in identifying occupational exposures in China
What information do you have/will you have from the study population?
– Make sure the detail of job and industry data matches with the JEM
How to use a JEM
Create the JEM before you gather the occupational history data
Code the job histories from subjects using the same method as in the JEM
Quality assurance Combine job history database
with JEM to provide exposure estimates
Software allows user to explore JEM sensitivity to various assumptions
How to collect occupational histories
Start at the beginning! Use trigger questions to gather more data on
particular exposures Use a timeline
– Family events (marriage, births, weddings)– National events (war, flooding, world cup!)
Ask about changes within a job Record as much data as possible about tasks, control
measures, frequency of use and indicators of exposure
Acute symptoms can be a marker of high exposures
Using a JEM in the Geoparkinson study Large multi-centre study of Genetic, Environmental and Occupational risk factors for
Parkinson’s Disease Population based case-control study (1000 cases/ 3000 controls) Hypothesis that solvents, pesticides and/or metal exposures may modify the risk of
developing PD. Quantitative JEM established prior to data collection Training of researchers in gathering occupational history data Detailed exposure specific questionnaires for jobs identified as having potential
exposure to agents of interest Modifiers generated for particular information Each individual’s exposure estimated using ‘base’ JEM estimate modified by expert
assessment using job description QA: repeat assessments (10%) and second assessor (10%) Allows capture of some degree of exposure variability within jobs Time consuming! http://www.abdn.ac.uk/deom/geop
So how good are JEMs?
Not very -but probably still better than self-reported exposures. Tielemans et al. 1999 examined JEM output with urinary markers
of solvent and metal exposures and demonstrated low levels of agreement (kappa 0.04-0.13) and low specificities and sensitivities.
JEMs do not have the means of accounting for variability in exposure within a job
Kromhout et al. 1993 showed that two-thirds of job titles had personal exposure measurements that spanned a ten-fold range.
Study-specific JEMs where the ‘base’ exposure assessment is modified by expert judgement of the job and task description are likely to be much more effective
Further reading Asthma JEM- freely available
http://www.cher.ubc.ca/asthmajem/index.htm ‘Exposure surrogates: job exposure matrices,
self reports and expert evaluation’ Kay Teschke Chapter 8 in Occupational and Environmental epidemiology. OUP, 2003.
Goldberg M, Kromhout H, Guenel P, et al. Job exposure matrices in industry. Int J Epidemiol. 1993;22 Suppl 2:S10-5.
Le Moual N, Bakke P, Orlowski E, et al. Performance of population specific job exposure matrices (JEMs): European collaborative analyses on occupational risk factors for chronic obstructive pulmonary disease with job exposure matrices (ECOJEM).Occup Environ Med. 2000 Feb;57(2):126-32.
