706 productivity loss, a reasonable proportion of productivity loss at work will occur due to non-health-related causes, for example machine breakdown, quality problems, and logis- tic problems (Schultz and Edington 2007; van den Heuvel et al. 2007). Also diVerent work characteristics, such as high physical work demands or high psychosocial work demands, may be related to productivity loss at work. For example, Alavinia et al. (2009) showed that lack of job control, adjusted for the presence of health problems with functional limitations, was associated with productivity loss at work (OR 1.36, 1.14–1.63). Among younger workers with upper extremity symptoms, a combination of high physical load as well as high job strain was also associated with productivity loss at work (Martimo et al. 2009). Therefore, work-related factors, such as high physical and psychosocial work demands, could be important for pro- ductivity loss at work, either through their direct inXuence on productivity or an indirect eVect through their inXuence on workers’ health. It is an important question whether the distinguished determinants of productivity loss act com- pletely independent from each other. It may be expected that in certain situations, workers with health problems or decreased work ability have possibilities to prevent produc- tivity loss at work (Geuskens et al. 2008; Alavinia et al. 2009; Böckerman and Laukkanen 2010). We hypothesize that work-related characteristics play an important role in supporting workers to remain productive, despite a decreased work ability. The research questions were (1) What is the association between decreased work ability and productivity loss at work? (2) What is the association between physical and psychosocial work demands and productivity loss at work? (3) What is the association between decreased work ability and productivity loss at work inXuenced by high physical or psychosocial workload? Methods Study population The study population consisted of 10,542 workers in 49 diVerent Dutch companies in the Netherlands in 2005– 2009. Companies from a whole range of sectors participated, i.e. commercial services (41%), non-commercial services (37%), industrial manufacturers (18%), and construction (4%). These companies had commissioned an occupational health organization to launch a program to investigate the work ability of the workforce and as part of this program a questionnaire survey was conducted on health, work demands, work ability, and productivity at work. Compa- nies participating in this program invited all their workers to participate. The occupational health organization had 123 Int Arch Occup Environ Health (2011) 84:705–712 send an invitation to all eligible workers by regular mail and provided them with an individualized password to Wll out the questionnaire on a secured Web site. At the time of enrolment, written informed consent was obtained from all participants. In the original study population, non-responders accounted for 7,905 subjects (42%). Some workers did not Wll out questions on productivity at work (0.8%), work abil- ity index (1.1%), or work-related factors (3.6%). Complete data on productivity loss at work, work ability, and work- related factors were present for 10,542 subjects (56%), which were made available to the Erasmus Productivity Loss at Work database (ELPW database). Productivity The main outcome of this study, productivity loss at work, was collected using the quantity scale of the quantity and quality (QQ) instrument (Brouwer et al. 1999). Respon- dents were asked to indicate how much work they had actu- ally performed during regular hours on their most recent regular workday relative to a normal workday. The quantity of productivity was measured on a 10-point numerical rat- ing scale with 0 representing “nothing” and 10 representing “normal quantity”. The outcome was dichotomized into those with productivity loss at work (score less than 10) and those without (productivity score = 10). The quality of pro- ductivity was not measured because the quality and quan- tity question is highly correlated (Meerding et al. 2005). Work ability index The work ability index (WAI) (Tuomi et al. 1998; Ilmarinen 2009) is a measure for the degree to which a worker, given his health, is physically and mentally able to cope with the demands at work. The WAI consists of an assessment of work ability relative to physical and mental work demands at this moment, diagnosed diseases, and limita- tions in work due to disease, sick leave over the past 12 months, work ability prognosis within 2 years, and psy- chological resources recently. The WAI constitutes of seven dimensions, the index being derived as the sum of the ratings on these dimensions. The range of the summative index is 7–49 classiWes work ability into poor (7–27), mod- erate (28–36), good (37–43), or excellent (44–49). Decreased work ability was deWned as a score lower than 37 (poor and moderate). Work-related factors The work-related factors in the questionnaire consisted of items on physical and psychosocial demands. Physical load in the current job concerned the regular presence of manual