Finnish Institute of Occupational Health, Thesis
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Estimating Future Employment Time Health State Transitions & Markku M. Nurminen Probability 0.2 0.4 0.6 0.8 1 0 2000 1995 1990 Year 1985 Probability 0.2 0.4 0.6 0.8 1 1980 0 20 30 40 50 60 2000 Age 1995 1990 Year 1985 1980 60 20 30 40 50 Age Helsinki 2008 Estimating Future Employment Time & Health State Transitions Markku M. Nurminen with Contributors Brett A. Davis Christopher R. Heathcote Tuula Nurminen Borek D. Puza Helsinki 2008 Publication information This publication consists of copyrighted works. It may be downloaded, displayed and printed for own personal use. Unless you have the permission of the copyright owner, you may not otherwise reproduce any of the contents. Commercial use is prohibited. The bibliographic reference is: Nurminen MM. Working Life Expectancy. Estimating Future Employment Time and Health State Transitions. Helsinki: Finnish Institute of Occupational Health, 2008. Online format: http://www.ttl.fi/Internet/English/Information/Electronic+publications/ ISBN 978-951-802-825-6 © Finnish Institute of Occupational Health 2008 Print format: ISBN 978-951-802-824-9 © Markku Nurminen 2008 Edita Prima Oy Helsinki 2008 Contact details Finnish Institute of Occupational Health Centre of Excellence for Good Practices and Competence Work and Society Team Topeliuksenkatu 41 a A FI-00250 Helsinki FINLAND Telephone: +358-30-4741 Email addresses: [email protected] [email protected] i Contents . i Preface . iii Abstract . v Résumés . vii Publications . ix Acknowledgments . xiii Introduction . 1 Research Background . 2 The Working Life Expectancy Project . 4 Objectives . 5 Recalling the Basic Principles . 5 Quantification of Working Life Developments . 6 Application of Methodological Advances . 7 Data . 9 Cohort Surveys . 9 Dynamic Population Censuses . 11 Methods . 13 Traditional Actuarial Approaches . 13 Modern Regression Approaches . 14 Results . 17 Occupation Probabilities . 17 Probability Surfaces . 18 Life and Working Life Expectancies . 21 Work Ability . 25 Labor Force Dynamics . 27 Fixed-Term Employment . 28 ii Discussion 33 On the Definition of Probability . 33 The Markov Property and Independence . 35 Multi-State Modelling for Transition Probabilities . 36 Estimating Working Life Expectancies . 37 Gender Inequalities in Working Life Course . 41 Foresight into Labour Force Transitions . 44 Relevance and Significance of the Research . 47 Conclusions . 49 Notes . 51 a. Boundaries of Probability . 51 b. Probability of Causation . 53 c. Smoker's Peril Problem . 55 Appendix . 59 Probabilities for Finnish Working Life Tables . 59 References . 63 PART I Reviews Paper 1 Paper 2 PART II Original Articles Paper 3 Paper 4 Paper 5 Paper 6 Paper 7 Paper 8 PART III Conference Proceedings Paper 9 Paper 10 Paper 11 Paper 12 iii In February 2001, the Board of Directors of the Finnish Institute of Occupational Health, headed by Director General, Prof. Jorma Rantanen, commissioned the Department of Epidemiology and Biostatistics to probe the suggestion of developing an indicator termed 'Work Ability Adjusted Life Years' as a measure of the quality of work life. The measure should take into account the proportion of years lived, having good work ability, and thus it would be in accordance with the widely- used summary measure of population health, viz. 'Disability Adjusted Life Years'. In the course of the subsequent three years of quite intensive pursuit, the initial plan and the actual project took shape with two distinctive objectives: first, the development of a statistic for the estimation of the future work ability and the duration of employment; and, second, the application of the statistic to survey data on ageing Finnish municipal workers and to the total Finnish employed population. At the outset of the project, in October 2001, I was fortunate to come across with a novel methodology in recently-published articles by the mathematical statisticians at the Australian National University, in Canberra, ACT, a research team lead by Emeritus Professor Christopher R. Heathcote. The seminal idea of this approach was to replace the traditional life table techniques that are based on frequency arguments by modern multivariate regression type arguments for modelling and estimation of employment and health state expectancies. The latter approach was originally developed for the analysis of sequential health surveys based on a multinomial model. For the purposes of this project, the method was refined and adapted for use in a working life situation. In the application of the methodology to Finnish occupational survey and population census data, the subject-matter issues of the project related to the themes of work ability, disability pensioning, early retirement and old-age retirement and mortality. It is the quantification of the durations stayed in these employment-health states, as well as transitions between the states that this project work was concerned with. In this context, a distinction was drawn between 'marginal' and 'conditional' iv probabilities and, thereby, expectancies. The latter depend on the initial state, that is, for example, whether a person is disabled or not at the given age for which the expectancy is calculated; longitudinal data are required in this case. On the other hand, marginal expectancies are those lacking such information. In 2005, the year when the new Finnish legislation on retirement was enacted, the produced information on the working life expectancies of Finns was deemed most timely and useful in consideration of the surveillance of working life conditions. Specific, previously unavailable information on the total duration of employment signed under fixed- term versus permanent contracts for the Finnish population in the decade 1997-2006 was worked out in 2007 and published in 2008. A continuation of the project to encompass the estimation of the transitions between occupational classes utilising the individually-linked Longitudinal Census File of Statistics Finland in the period 1995 through 2005 is currently underway. The purpose of this thesis compendium is dual: first, to bring to the fore for researchers engaged in similar quantifications in the health fields, in a single volume, the reviews and original articles that appeared in international statistical, epidemiological and occupational health journals; and second, to present information for societal planners and public decision-makers of the estimates and inferences that this project produced on work ability and duration of active employment germane to the Finnish labour force under transition. Markku Nurminen May 2008 v In this thesis, stochastic process analysis is applied for estimating the future employment time and health state movements in the Finnish population. The interdisciplinary study is based on formal demographic and applied statistical methodology, whilst the observed data originate from a longitudinal cohort study in the field of occupational epidemiology and from annual official statistics on employment, as well as other states such as work disability, retirement, and death. For the purpose of this research, an indicator was introduced, termed working life expectancy. It measures the expected duration of a person's working life, starting from a given age until the end of his or her vocational career. Unlike the analogous concept of life expectancy, working life expectancy is estimated from the time spans that an individual is actually employed. These periods can be consecutive or interruptive spells of contract work, as in fixed-term employment relationships. Nowadays, a working career is rarely a continuous stretch of time throughout a person’s entire working life, lasting from first entry to employment until final retirement. Yet the prevailing practices of quantifying trends in the duration of working career do not keep with the first principles of modern, multistate regression methods. The new developed techniques permitted a consistent estimation of the marginal probabilities that a person occupies a given work-health state or the transition probabilities between the states and thereby the expectancies. Under a non-homogeneous discrete time Markov process model, the estimation of transition probabilities can be conditioned on the initial work ability state, and to assess its effect on the subsequent occupation times and first passage times to other states. The particular age-, gender-, and period-specific data analyses focused on: a cohort of aging municipal employees, with eleven years of follow-up, including three surveys in 1981, 1985, 1992; the total Finnish employed labour force, based on annual censuses from 1980 to 2001, and a forecast for 2006; and the comparison of fixed-term Finnish employees to permanently employed people during 1997-2006. vi The study produced unique estimates of the working life expectancies, which can be used as a scientifically based and unbiased source of societal information, to gain insight to the present state and to tentatively forecast the future development of the Finnish labour force under transition. vii Markku Mikael Nurminen, MA (Mathematics), LicPolSc, PhD (Statistics), University of Helsinki, Finland, and DSc (Epidemiology, dissertation approved with honours), University of Tampere, Finland, is currently Senior Research Scientist at the Finnish Institute of Occupational Health (FIOH) and Adjunct Professor in Biometry at the Department of Public Health, Faculty of Medicine, University of Helsinki. He has scientific qualifications required for the post of Associate