World Health Organization NI Regional Office for EuropeVlIs;,, âj Copenhagen ` Epidemiology of occupational health WHO Regional Publications, European Series No. 20 The World Health Organization is a specialized agency of the United Nations with primary responsibility for international health matters and public health. Through this Organization, which was created in 1948, the health professions of some 160 countries exchange their knowledge and experience with the aim of making possible the attainment by all citizens of the world by the year 2000 of a level of health that will permit them to lead a socially and economically productive life. The WHO Regional Office for Europe is one of six regional offices throughout the world, each with its own programme geared to the particular health problems of the countries it serves. The European Region has 32 active Member States,a and is unique in that a large proportion of them are industrialized countries with highly advanced medical services. The European programme therefore differs from those of other regions in concentrating on the problems associated with industrial society. In its strategy for attaining the goal of "health for all by the year 2000" the Regional Office is arranging its activities in three main areas: promotion of lifestyles conducive to health; reduction of preventable conditions; and provision of care that is ade- quate, accessible and acceptable to all. The Region is also characterized by the large number of languages spoken by its peoples, and the resulting difficulties in disseminating information to all who may need it. The Regional Office publishes in four languages - English, French, German and Russian - and applications for rights of translation into other languages are most welcome. a Albania, Austria, Belgium, Bulgaria, Czechoslovakia, Denmark, Finland, France, German Demo- cratic Republic, Federal Republic of Germany, Greece, Hungary, Iceland, Ireland, Israel, Italy, Luxem- bourg, Malta, Monaco, Netherlands. Norway, Poland, Portugal, Romania, San Marino, Spain, Sweden, Switzerland, Turkey, USSR, United Kingdom and Yugoslavia. Epidemiology of occupational health Cover photo by courtesy of the Department of Occupational Medicine, Regional Hospital, Örebro, Sweden. World Health Organization Office for Europe ( (11, ) Copenhagenâ Epidemiology of occupational health Edited by M. Karvonen and M.I. Mikheev WHO Regional Publications, European Series No. 20 ISBN 92 890 1111 4 ISSN 0378 -2255 © World Health Organization 1986 Publications of the World Health Organization enjoy copyright protection in accord- ance with the provisions of Protocol 2 of the Universal Copyright Convention. For rights of reproduction or translation, in part or in toto, of publications issued by the WHO Regional Office for Europe application should be made to the Regional Office for Europe, Scherfigsvej 8, DK -2100 Copenhagen 0, Denmark. The Regional Office welcomes such applications. The designations employed and the presentation of the material in this publi- cation do not imply the expression of any opinion whatsoever on the part of the Secretariat of the World Health Organization concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. The mention of specific companies or of certain manufacturers' products does not imply that they are endorsed or recommended by the World Health Organiz- ation in preference to others of a similar nature that are not mentioned. Errors and omissions excepted, the names of proprietary products are distinguished by initial capital letters. The views expressed in this publication are those of the authors and do not necessarily represent the decisions or the stated policy of the World Health Organization. CONTENTS Page Preface vii Independent reviewers ix 1. Epidemiology in the context of occupational health - M. Karvonen 2.Nature and health effects of occupational factors - N.F. lzmerov & J.I. Kundiev 17 3. Work, health and disease - G. Kazantzis & J.C. McDonald 43 4. Evaluation of the long -term effects of harmful occupational factors - M.1. Mikheev 69 5. Sources of data - R.S.F. Schilling 81 6. Screening in the assessment of health risks - T. Popov 97 7. Descriptive epidemiology -J. Indulski 119 8. Cross -sectional studies -H. Thiele & G. Enderlein 135 9.The cohort study -W. Halperin et al. 149 10. Case -control studies, with a note on proportional mortality evaluation - O. Axelson 181 11. Study of combined effects - J.I. Kundiev & A.O. Navakatikyan 209 12. Assessment of occupational stress - R. Kalimo 231 13. Statistical analysis of epidemiological data: an overview of some basic considerations -M. Nurminen 251 14. Validity aspects of epidemiological studies - S. Hernberg 269 15. Experimental epidemiology - P. Lazar 283 16. Accident epidemiology -J. Saari 299 v 17. Uses of epidemiology in occupational health - S. Hernberg 317 18. Reappraisal of an epidemiological study - M. Nurminen 341 Glossary of terms 375 vi Preface Many definitions of epidemiology have emerged over the last few decades, in keeping with the rapid development and broadening of the science. According to the Dictionary of epidemiology edited by John M. Last in 1983, epidemi- ology is" the study of the distribution and determinants of health -related states and events in populations, and the application of this study to control of health problems ". Epidemiological methods have been widely used in the field of occupational health to describe the health status of specific working popu- lations, to study their morbidity in relation to the type of occupation, to identify specific occupational hazards, to generate and test hypotheses on cause -effect relationships, and to evaluate interventions. When the relationship has proved to be quite strong and specific, such studies have been very successful in increasing our knowledge of the effects of occupational hazards. In many cases, however, epidemiological studies have led to controversial and confusing results. This may have been due to the use of inappropriate methodology, but may also have been the result of overestimating the power of epidemiological and statistical methods. Those engaged in resource consuming studies must be well aware of the limitations of the tools they are using. In the particular field of occupational health there are limitations due to the characteristics of the population under study, which is usually rather small, selected, and subject to change over time with regard to exposure to occupational hazards. Other limitations arise from the type of hazards concerned, very often combined with other exposures that may or may not be related to occupation, and also with long latency periods for any outcome from the exposures. In addition, there are methodological limitations due to the lack of proper assessment of exposure and health effects. Retrospective studies may be subject to inappropriate information on exposure to the suspected hazard, as well as to other confound- ing environmental or behavioural factors. Prospective studies may overcome this type of problem but, besides their relatively high cost, they have their own methodological biases too, such as those linked to the quality of the reference groups, observer errors, and changes induced in the study population by the study itself. Such limitations should not be seen as an obstacle to the use of epidemi- ology, but rather as justification of the use of sound and standardized methods. The present manual tries to respond to the specific needs of occupational health vii epidemiology. The WHO Regional Office for Europe, after a decade of work in this field, has secured the collaboration of leading experts to present and discuss in a practical way different approaches and methods and their appli- cation to specific problems in occupational health. Rather than a comprehen- sive review of the subject, the book presents a series of articles. The first four chapters deal with general principles and definitions in occupational epidemi- ology, and describe the work- related hazards and diseases. Chapters 5, 6 and 7 deal with information collection and the use of data in the assessment of health risks and in descriptive epidemiology. General methods for epidemiological studies are discussed in Chapters 8 -10. The following chapters address specific aspects such as the study of combined effects (Chapter 11), the statistical analysis of epidemiological data (Chapter 13), the validity aspects of epidemio- logical studies, including consideration on the problems of "false positive" and "false negative" results and the basis for causality judgement (Chapter 14), or the particular interest of experimental epidemiology in occupational health (Chapter 15). Chapters 12 and 16 cover two special issues of importance to workers' health, namely occupational stress and the epidemiology of accidents. Chapter 17 gives an excellent overview of the uses of epidemiology in occu- pational health, and the last chapter presents a concrete case study, with an assessment of the use made of epidemiological methods. There are unavoidable repetitions and overlaps throughout this manual due to the way in which it was compiled, but it gives very useful and practical information to those interested in epidemiological research applied to occupational problems. All this work was done in collaboration with the office of occupational health at WHO headquarters in Geneva. It is hoped that this book will