The measurements of sickness absence – a theoretical perspective

Abstract

The assessment of sickness absence is a challenge in spite of accessible numbers of spells, persons, and days of absence in public and employer registers. Concepts and their definitions are still to a small extent standardized, and clear and explicit definitions need to be provided. In epidemiological studies, the definition of the study base is important, and in sickness absence research a prerequisite is that an individual belongs to a sickness absence insurance scheme. Population at risk can be identified at three levels: the general population, the sickness insured population, and the sickness absent population. Cases in sickness absence studies can be quantified in terms of spell-, person-, or time based measurements. Each of these ways reflects different contents of sickness absence as a phenomenon, and the choice of measurement should be guided by the purpose of the study as well as the target area. Five different measurements (frequency, length, cumulative incidence, incidence rate, and duration) are suggested and their application is discussed. These five measurements can be seen as a summary of measurements used in different studies and an application of epidemiologic methods into sickness absence research. There are opportunities to increase the quality of sickness absence research, with an increased awareness of the importance of the measurements used.