Exposure matrices: how to create them, how to use them, and what they can tell us

1. Exposure matrices: how to create them, how to use them, and what they can tell us Dr Sean Semple Department of Environmental & Occupational Medicine University of Aberdeen Scotland

2. 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?

3. 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

4. A simple ever/never JEM…

5. A quantitative JEM… 0= no exposure; 1= low exposure; 2=medium exposure; 3= high exposure

6. A JEM with intensity and frequency… 0= no exposure; 1= low exposure; 2=medium exposure; 3= high exposure 1= rare event; 2=sporadic event; 3= regular event

7. 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

8. 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

9. 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.

10. SOC • SOC 2000 Standard Occupational Classification • 9 major groups • 25 sub-major groups • 81 minor groups • 353 Unit groups 1   Managers and Senior Officials 2   Professional Occupations 3   Associate Professional and Technical Occupations 4   Administrative and Secretarial Occupations 5   Skilled Trades Occupations 6   Personal Service Occupations 7   Sales and Customer Service Occupations 8   Process, Plant and Machine Operatives 9   Elementary Occupations

11. SIC(92) Aagriculture, hunting and forestry Bfishing Cmining and quarrying Dmanufacturing Eelectricity, gas and water supply Fconstruction Gwholesale and retail trade; Repair of motor vehicles, motorcycles and personal and household goods Hhotels and restaurants Itransport, storage and communication Jfinancial intermediation Kreal estate, renting and business activities Lpublic administration and defence; Compulsory social security Meducation Nhealth and social work Oother community, social & personal service activities Pprivate households with employed persons Qextra - territorial organisations and bodies • Standard Industrial Classification of Economic Activities • 17 sections • 16 subsections • 60 divisions • 222 groups • 503 classes • 253 subclasses

12. 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/

13. 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?

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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.

20. Contact details sean.semple@abdn.ac.uk www.abdn.ac.uk/deom