Precision and accuracy in measuring absence from work as a basis for calculating productivity costs in The Netherlands

The impact of disease on the ability of a person to perform work should be part of an economic evaluation when a societal viewpoint is used for the an alysis. This impact is reflected by calculating productivity costs. Measure ment of these costs is often performed retrospectively. The purpose of our study was to study precision and accuracy of a retrospective self-administe red questionnaire on sick leave. Employees of a company were asked to indic ate the number of days absent from work due to illness during the past 2 we eks, 4 weeks, 2 months, 6 months, and the past 12 months. The percentage of respondents with an absolute difference of a maximum of respectively 0. 1, 2, 3, 4, 5, 6, 7, 8, and 9 or more days between reported, and company-regi stered absence due to illness was determined. Besides this, the proportiona l difference was calculated. A systematic difference was tested with a sign ed rank test. Of the reported data, 95% matched the registered data perfect ly when the recall period was limited to 2 and 4 weeks. This percentage dec reased to 87%, 57%, and 51% for 2 months, 6 months, and 12 months. The weig hted mean proportional differences for the recall periods were respectively 32.9, 35.2, 45.3, 34.9, and 113.6%. No systematic positive or negative dif ference was found between registered and reported sick leave. The results s uggest that the recall period for retrospective measurement of sick leave i s limited according to the precision level, which seems to be appropriate f or the subject and the purpose of the study. We recommend using a recall pe riod of no more than 3 months. (C) 2000 Elsevier Science Ltd. All rights re served.