Abstract
Recent reviews show that self-reported psychosocial factors related to work, such as job demands and job control, are associated with employee mental health, but it is not known whether this association is attributable to reporting bias. The authors examined this question using objectively measured hospital ward overcrowding as an instrument. The extent of overcrowding provided a strong instrument for self-reported job demands but not for job control, and it was used to examine unbiased associations between self-reported job demands and sickness absence with a psychiatric diagnosis among 2,784 female nurses working in somatic illness wards in Finland. During the 12-month follow-up period (2004-2005), 102 nurses had an absence with a psychiatric diagnosis, 33 with a diagnosis of depressive disorder. Both greater extent of overcrowding and higher self-reported job demands were associated with increased risk of psychiatric absence. The latter association was stronger but less precisely estimated in an instrumental-variables analysis which took into account only the variation in self-reported job demands that was explained by overcrowding. Repeating these analyses with absence due to depressive disorders as the outcome led to similar results. Findings from this instrumental-variables analysis support the status of high self-reported job demands as a risk factor for absence with a psychiatric diagnosis.