Monday, 28 February 2011 21:03

Summary Worklife Exposure Measures

Rate this item
(1 Vote)

Researchers are fortunate when they have at their disposal a detailed chronology of the worklife experience of workers that provides an historic review of jobs they have held over time. For these workers a job exposure matrix can then be set up that allows each and every job change that a worker has gone through to be associated with specific exposure information.

Detailed exposure histories must be summarized for analysis purposes in order to determine whether patterns are evident that could be related to health and safety issues in the workplace. We can visualize a list of, say, 20 job changes that a worker had experienced in his or her working lifetime. There are then several alternative ways in which the exposure details (for each of the 20 job changes in this example) can be summarized, taking duration and/or concentration/dose/grade of exposure into account.

It is important to note, however, that different conclusions from a study could be reached depending on the method selected (Suarez-Almazor et al. 1992). An example of five summary worklife exposure measures is shown in table 1.

Table 1. Formulae and dimensions or units of the five selected summary measures of worklife exposure

Exposure measure



Cumulative exposure index (CEI)

Σ (grade x time exposed)

grade and time

Mean grade (MG)

Σ (grade x time exposed)/total time exposed


Highest grade ever (HG)

highest grade to which exposed for ≥ 7 days


Time-weighted average (TWA) grade

Σ (grade x time exposed)/total time employed


Total time exposed (TTE)

Σ time exposed


Adapted from Suarez-Almazor et al. 1992.

Cumulative exposure index. The cumulative exposure index (CEI) is equivalent to “dose” in toxicological studies and represents the sum, over a working lifetime, of the products of exposure grade and exposure duration for each successive job title. It includes time in its units.

Mean grade. The mean grade (MG) cumulates the products of exposure grade and exposure duration for each successive job title (i.e., the CEI) and divides by the total time exposed at any grade greater than zero. MG is independent of time in its units; the summary measure for a person exposed for a long period at a high concentration will be similar to that for a person exposed for a short period at a high concentration. Within any matched set in a case-control design, MG is an average grade of exposure per unit of time exposed. It is an average grade for the time actually exposed to the agent under consideration.

Highest grade ever. The highest grade ever (HG) is determined from scanning the work history for the highest grade assignment in the period of observation to which the worker was exposed for at least seven days. The HG could misrepresent a person’s worklife exposure because, by its very formulation, it is based on a maximizing rather than on an averaging procedure and is therefore independent of duration of exposure in its units.

Time-weighted average grade. The time-weighted average (TWA) grade is the cumulative exposure index (CEI) divided by the total time employed. Within any matched set in a case-control design, the TWA grade averages over total time employed. It differs from MG, which averages only over the total time actually exposed. Thus, TWA grade can be viewed as an average exposure per unit of time in the full term of employment regardless of exposure per se.

Total time exposed. The total time exposed (TTE) accumulates all time periods associated with exposure in units of time. TTE has appeal for its simplicity. However, it is well accepted that health effects must be related not only to duration of chemical exposure, but also to the intensity of that exposure (i.e., the concentration or grade).

Clearly, the utility of a summary exposure measure is determined by the respective weight it attributes to either duration or concentration of exposure or both. Thus different measures may produce different results (Walker and Blettner 1985). Ideally, the summary measure selected should be based on a set of defensible assumptions regarding the postulated biological mechanism for the agent or disease association under study (Smith 1987). This procedure is not, however, always possible. Very often, the biological effect of the duration of exposure or the concentration of the agent under study is unknown. In this context, the use of different exposure measures may be useful to suggest a mechanism by which exposure exerts its effect.

It is recommended that, in the absence of proved models for assessing exposure, a variety of summary worklife exposure measures be used to estimate risk. This approach would facilitate the comparison of findings across studies.



Read 5662 times Last modified on Thursday, 13 October 2011 20:25

" DISCLAIMER: The ILO does not take responsibility for content presented on this web portal that is presented in any language other than English, which is the language used for the initial production and peer-review of original content. Certain statistics have not been updated since the production of the 4th edition of the Encyclopaedia (1998)."


Epidemiology and Statistics References

Ahlbom, A. 1984. Criteria of causal association in epidemiology. In Health, Disease, and Causal Explanations in Medicine, edited by L Nordenfelt and BIB Lindahl. Dordrecht: D Reidel.

American Conference of Government Industrial Hygienists (ACGIH). 1991. Exposure Assessment for Epidemiology and Hazard Control, edited by SM Rappaport and TJ Smith. Chelsea, Mich.:Lewis.

Armstrong, BK, E White, and R Saracci. 1992. Principles of Exposure Measurement in Epidemiology. Oxford: Oxford Univ. Press.

Ashford, NA, CI Spadafor, DB Hattis, and CC Caldart. 1990. Monitoring the Worker for Exposure and Disease. Baltimore: Johns Hopkins Univ. Press.

Axelson, O. 1978. Aspects on confounding in occupational health epidemiology. Scand J Work Environ Health 4:85-89.

—. 1994. Some recent developments in occupational epidemiology. Scand J Work Environ Health 20 (Special issue):9-18.

Ayrton-Paris, JA. 1822. Pharmacologia.

Babbie, E. 1992. The Practice of Social Research. Belmont, Calif.: Wadsworth.

Beauchamp, TL, RR Cook, WE Fayerweather, GK Raabe, WE Thar, SR Cowles, and GH Spivey. 1991. Ethical Guidelines for Epidemiologists. J Clin Epidemiol 44 Suppl. I:151S-169S.

Bell, B. 1876. Paraffin epithelioma of the scrotum. Edinburgh Med J 22:135.

Blondin, O and C Viau. 1992. Benzo(a)pyrene-blood protein adducts in wild woodchucks used as biological sentinels of environmental polycyclic aromatic hydrocarbons contamination. Arch Environ Contam Toxicol 23:310-315.

Buck, C. 1975. Popper’s philosophy for epidemiologists. Int J Epidemiol 4:159-168.

Case, RAM and ME Hosker. 1954. Tumour on the urinary bladder as an occupational disease in the rubber industry in England and Wales. Brit J Prevent Soc Med 8:39-50.

Checkoway, H, NE Pearce, and DJ Crawford-Brown. 1989. Research Methods in Occupational Epidemiology. New York: Oxford Univ. Press.

Clayson, DB. 1962. Chemical Carcinogenesis. London: JA Churchill.

Clayton, D. 1992. Teaching statistical methods in epidemiology. In Epidemiology. What You Should Know and What You Could Do, edited by J Olsen and D Trichopoulos. Oxford: Oxford Univ. Press.

Clayton, D and M Hills. 1993. Statistical Models in Epidemiology. New York: Oxford Univ. Press.

Cornfield, J. 1954. Statistical relationships and proof in medicine. Am Stat 8:19-21.

Council for International Organizations of Medical Sciences (CIOMS). 1991. International Guidelines for Ethical Review of Epidemiologic Studies. Geneva: CIOMS.

Czaja, R and J Blair. 1996. Designing Surveys. Thousand Oaks, Calif: Pine Forge Press.

Doll, R. 1952. The causes of death among gas-workers with special reference to cancer of the lung. Brit J Ind Med 9:180-185.

—. 1955. Mortality from lung cancer in asbestos workers. Brit J Ind Med 12:81-86.

Droz, PO and MM Wu. 1991. Biological monitoring strategies. In Exposure Assessment for Epidemiology and Hazard Control, edited by SM Rappaport and TJ Smith. Chelsea, Mich.: Lewis.

Gamble, J and R Spirtas. 1976. Job classification and utilization of complete work histories in occupational epidemiology. J Med 18:399-404.

Gardner, MJ and DG Altman. 1989. Statistics With Confidence. Confidence Intervals and Statistical Guidelines. London: BMJ Publishing House.

Garfinkel, L. 1984. Classics in oncology; E. Cuyler Hammond, ScD. Ca-Cancer Journal for Clinicians. 38(1): 23-27

Giere, RN. 1979. Understanding Scientific Reasoning. New York: Holt Rinehart & Winston.

Glickman, LT. 1993. Natural exposure studies in pet animals: Sentinels for environmental carcinogens. Vet Can Soc Newslttr 17:5-7.

Glickman, LT, LM Domanski, TG Maguire, RR Dubielzig, and A Churg. 1983. Mesothelioma in pet dogs associated with exposure of their owners to asbestos. Environmental Research 32:305-313.

Gloyne, SR. 1935. Two cases of squamous carcinoma of the lung occurring in asbestosis. Tubercle 17:5-10.

—. 1951. Pneumoconiosis: Histological survey of necropsy material in 1,205 cases. Lancet 1:810-814.

Greenland, S. 1987. Quantitative methods in the review of epidemiological literature. Epidemiol Rev 9:1-30.

—. 1990. Randomization, statistics, and causal inference. Epidemiology 1:421-429.

Harting, FH and W Hesse. 1879. Der Lungenkrebs, die bergkrankheit in den Schneeberger Gruben. Vierteljahrsschr Gerichtl Med Offentl Gesundheitswesen CAPS 30:296-307.

Hayes, RB, JW Raatgever, A de Bruyn, and M Gerin. 1986. Cancer of the nasal cavity and paranasal sinuses, and formaldehyde exposure. Int J Cancer 37:487-492.

Hayes, HM, RE Tarone, HW Casey, and DL Huxsoll. 1990. Excess of seminomas observed in Vietnam service US military working dogs. J Natl Cancer Inst 82:1042-1046.

Hernberg, S. 1992. Introduction to Occupational Epidemiology. Chelsea, Mich.: Lewis.
Hill, AB. 1965. The environment and disease: Association or causation? Proc Royal Soc Med 58:295-300.

Hume, D. 1978. A Treatise of Human Nature. Oxford: Clarendon Press.

Hungerford, LL, HL Trammel, and JM Clark. 1995. The potential utility of animal poisoning data to identify human exposure to environmental toxins. Vet Hum Toxicol 37:158-162.

Jeyaratnam, J. 1994. Transfer of hazardous industries. In Occupational Cancer in Developing Countries, edited by NE Pearce, E Matos, H Vainio, P Boffetta, and M Kogevinas. Lyon: IARC.

Karhausen, LR. 1995. The poverty of Popperian epidemiology. Int J Epidemiol 24:869-874.

Kogevinas, M, P Boffetta, and N Pearce. 1994. Occupational exposure to carcinogens in developing countries. In Occupational Cancer in Developing Countries, edited by NE Pearce, E Matos, H Vainio, P Boffetta, and M Kogevinas. Lyon: IARC.

LaDou, J. 1991. Deadly migration. Tech Rev 7:47-53.

Laurell, AC, M Noriega, S Martinez, and J Villegas. 1992. Participatory research on workers’ health. Soc Sci Med 34:603-613.

Lilienfeld, AM and DE Lilienfeld. 1979. A century of case-control studies: progress? Chron Dis 32:5-13.

Loewenson, R and M Biocca. 1995. Participatory approaches in occupational health research. Med Lavoro 86:263-271.

Lynch, KM and WA Smith. 1935. Pulmonary asbestosis. III Carcinoma of lung in asbestos-silicosis. Am J Cancer 24:56-64.

Maclure, M. 1985. Popperian refutation in epidemiolgy. Am J Epidemiol 121:343-350.

—. 1988. Refutation in epidemiology: Why else not? In Causal Inference, edited by KJ Rothman. Chestnut Hill, Mass.: Epidemiology Resources.

Martin, SW, AH Meek, and P Willeberg. 1987. Veterinary Epidemiology. Des Moines: Iowa State Univ. Press.

McMichael, AJ. 1994. Invited commentary -"Molecular epidemiology": New pathway or new travelling companion? Am J Epidemiol 140:1-11.

Merletti, F and P Comba. 1992. Occupational epidemiology. In Teaching Epidemiology. What You Should Know and What You Could Do, edited by J Olsen and D Trichopoulos. Oxford: Oxford Univ. Press.

Miettinen, OS. 1985. Theoretical Epidemiology. Principles of Occurrence Research in Medicine. New York: John Wiley & Sons.

Newell, KW, AD Ross, and RM Renner. 1984. Phenoxy and picolinic acid herbicides and small-intestinal adenocarcinoma in sheep. Lancet 2:1301-1305.

Olsen, J, F Merletti, D Snashall, and K Vuylsteek. 1991. Searching for Causes of Work-Related Diseases. An Introduction to Epidemiology At the Work Site. Oxford: Oxford Medical Publications, Oxford Univ. Press.

Pearce, N. 1992. Methodological problems of time-related variables in occupational cohort studies. Rev Epidmiol Med Soc Santé Publ 40 Suppl: 43-54.

—. 1996. Traditional epidemiology, modern epidemiology and public health. Am J Public Health 86(5): 678-683.

Pearce, N, E Matos, H Vainio, P Boffetta, and M Kogevinas. 1994. Occupational cancer in developing countries. IARC Scientific Publications, no. 129. Lyon: IARC.

Pearce, N, S De Sanjose, P Boffetta, M Kogevinas, R Saracci, and D Savitz. 1995. Limitations of biomarkers of exposure in cancer epidemiology. Epidemiology 6:190-194.

Poole, C. 1987. Beyond the confidence interval. Am J Public Health 77:195-199.

Pott, P. 1775. Chirurgical Observations. London: Hawes, Clarke & Collins.

Proceedings of the Conference on Retrospective Assessment of Occupational Exposures in Epidemiology, Lyon, 13-15 April, 1994. 1995. Lyon: IARC .

Ramazzini, B. 1705. De Morbis Artificum Diatriva. Typis Antonii Capponi. Mutinae, MDCC. London: Andrew Bell & Others.

Rappaport, SM, H Kromhout, and E Symanski. 1993. Variation of exposure between workers in homogeneous exposure groups. Am Ind Hyg Assoc J 54(11):654-662.

Reif, JS, KS Lower, and GK Ogilvie. 1995. Residential exposure to magnetic fields and risk of canine lymphoma. Am J Epidemiol 141:3-17.

Reynolds, PM, JS Reif, HS Ramsdell, and JD Tessari. 1994. Canine exposure to herbicide-treated lawns and urinary excretion of 2,4-dichlorophenoxyacetic acid. Canc Epidem, Biomark and Prevention 3:233-237.

Robins, JM, D Blevins, G Ritter, and M Wulfsohn. 1992. G-estimation of the effect of prophylaxis therapy for pneumocystis carinii pneumonia on the survival of Aids patients. Epidemiology 3:319-336.

Rothman, KJ. 1986. Modern Epidemiology. Boston: Little, Brown & Co.

Saracci, R. 1995. Epidemiology: Yesterday, today, tomorrow. In Lectures and Current Topics in Epidemiology. Florence: European Educational Programme in Epidemiology.

Schaffner, KF. 1993. Discovery and Explanation in Biology and Medicine. Chicago: Univ. of Chicago Press.

Schlesselman, JJ. 1987. “Proof” of cause and effect in epidemiologic studies: Criteria for judgement. Prevent Med 16:195-210.

Schulte, P. 1989. Interpretation and communcication of the results of medical field investigations. J Occup Med 31:5889-5894.

Schulte, PA, WL Boal, JM Friedland, JT Walker, LB Connally, LF Mazzuckelli, and LJ Fine. 1993. Methodological issues in risk communications to workers. Am J Ind Med 23:3-9.

Schwabe, CW. 1993. The current epidemiological revolution in veterinary medicine. Part II. Prevent Vet Med 18:3-16.

Seidman, H, IJ Selikoff, and EC Hammond. 1979. Short-term asbestos work exposure and long-term observation. Ann NY Acad Sci 330:61-89.

Selikoff, IJ, EC Hammond, and J Churg. 1968. Asbestos exposure, smoking and neoplasia. JAMA 204:106-112.

—. 1964. Asbestos exposure and neoplasia. JAMA 188, 22-26.

Siemiatycki, J, L Richardson, M Gérin, M Goldberg, R Dewar, M Désy, S Campbell, and S Wacholder. 1986. Associations between several sites of cancer and nine organic dusts: Results from an hypothesis-generating case-control study in Montreal, 1979-1983. Am J Epidemiol 123:235-249.

Simonato, L. 1986. Occupational cancer risk in developing countries and priorities for epidemiological research. Presented at International Symposium On Health and Environment in Developing Countries, Haicco.

Smith, TJ. 1987. Exposure asssessment for occupational epidemiology. Am J Ind Med 12:249-268.

Soskolne, CL. 1985. Epidemiological research, interest groups, and the review process. J Publ Health Policy 6(2):173-184.

—. 1989. Epidemiology: Questions of science, ethics, morality and law. Am J Epidemiol 129(1):1-18.

—. 1993. Introduction to misconduct in science and scientific duties. J Expos Anal Environ Epidemiol 3 Suppl. 1:245-251.

Soskolne, CL, D Lilienfeld, and B Black. 1994. Epidemiology in legal proceedings in the United States. In The Identification and Control of Environmental and Occupational Diseases. Advances in Modern Environmental Toxicology: Part 1, edited by MA Mellman and A Upton. Princeton: Princeton Scientific Publishing.

Stellman, SD. 1987. Confounding. Prevent Med 16:165-182.

Suarez-Almazor, ME, CL Soskolne, K Fung, and GS Jhangri. 1992. Empirical assessment of the effect of different summary worklife exposure measures on the estimation of risk in case-referent studies of occupational cancer. Scand J Work Environ Health 18:233-241.

Thrusfield, MV. 1986. Veterinary Epidemiology. London: Butterworth Heinemann.

Trichopoulos, D. 1995. Accomplishments and prospects of epidemiology. In Lectures and Current Topics in Epidemiology. Florence: European Educational Programme in Epidemiology.

Van Damme, K, L Cateleyn, E Heseltine, A Huici, M Sorsa, N van Larebeke, and P Vineis. 1995. Individual susceptibility and prevention of occupational diseases: scientific and ethical issues. J Exp Med 37:91-99.

Vineis, P. 1991. Causality assessment in epidemiology. Theor Med 12:171-181.

Vineis, P. 1992. Uses of biochemical and biological markers in occupational epidemiology. Rev Epidmiol Med Soc Santé Publ 40 Suppl 1: 63-69.

Vineis, P and T Martone. 1995. Genetic-environmental interactions and low-level exposure to carcinogens. Epidemiology 6:455-457.

Vineis, P and L Simonato. 1991. Proportion of lung and bladder cancers in males resulting from occupation: A systematic approach. Arch Environ Health 46:6-15.

Vineis, P and CL Soskolne. 1993. Cancer risk assessment and management: An ethical perspective. J Occup Med 35(9):902-908.

Vineis, P, H Bartsch, N Caporaso, AM Harrington, FF Kadlubar, MT Landi, C Malaveille, PG Shields, P Skipper, G Talaska, and SR Tannenbaum. 1994. Genetically based N-acetyltransferase metabolic polymorphism and low level environmental exposure to carcinogens. Nature 369:154-156.

Vineis, P, K Cantor, C Gonzales, E Lynge, and V Vallyathan. 1995. Occupational cancer in developed and developing countries. Int J Cancer 62:655-660.

Von Volkmann, R. 1874. Ueber Theer-und Russkrebs. Klinische Wochenschrift 11:218.

Walker, AM and M Blettner. 1985. Comparing imperfect measures of exposure. Am J Epidemiol 121:783-790.

Wang, JD. 1991. From conjectures and refutation to the documentation of occupational diseases in Taiwan. Am J Ind Med 20:557-565.

—. 1993. Use of epidemiologic methods in studying diseases caused by toxic chemicals. J Natl Publ Health Assoc 12:326-334.

Wang, JD, WM Li, FC Hu, and KH Fu. 1987. Occupational risk and the development of premalignant skin lesions among paraquat manufacturers. Brit J Ind Med 44:196-200.

Weed, DL. 1986. On the logic of causal inference. Am J Epidemiol 123:965-979.

—. 1988. Causal criteria and popperian refutation. In Causal Inference, edited by KJ Rothman. Chestnut Hill, Mass.: Epidemiology Resources.

Wood, WB and SR Gloyne. 1930. Pulmonary asbestosis. Lancet 1:445-448.

Wyers, H. 1949. Asbestosis. Postgrad Med J 25:631-638.