2007), predominating underestimation (Burdorf and Laan 1991), and deviations in both directions in one sample (Jensen et al. 2000). Thus, the assessment behaviour may depend on the wording of the questionnaire, the study sample, or the exposure level (Barrero et al. 2009). As this study indicates, exposure level seems to have an enormous impact on the validity of self-reported knee exposure. In both surveys, Vorinostat order differences between reported and recorded durations of knee postures were small at a low exposure level but increased with increasing

exposure. Participants were able both to report the absence of knee postures exactly and to assess short time exposure, especially by comparing absolute values (see Bland–Altman plots) Tucidinostat in vitro rather than relative ones. On the other hand, high-exposed subjects were misjudging their amount of knee loading by far. Confirming this effect, a study on the duration of computer use of 87 computer workers reports comparable assessment behaviour for low- and high-exposed subjects (Heinrich et al. 2004). But in contrast, another study on that topic gives an opposite VS-4718 result: agreement between self-reported and observed duration of computer

use of 572 office workers improved with increasing exposure (IJmker et al. 2008). This effect might be explained by the use of categorical data (seven response categories for hours of computer use per day), while we used continuous data for assessment in our study. With respect to occupational knee load, only one of the cited studies took assessment behaviour of low- and high-exposed subjects into consideration (Klußmann et al. 2010). In a sub-analysis of this study, high-exposed workers showed a better ability to assess their exposure than low-exposed. However, study sample was rather small (n = 25) and deviations between mafosfamide both methods were only reported as relative differences instead of absolute numbers;

thus, the effect may be overestimated. Impact of knee disorders on the validity of self-reports The present study gave no hint of a differential misclassification of exposure due to self-reported knee complaints. Participants both with and without such complaints showed comparable assessment behaviour. This result seems to be contrary to studies reporting differential misclassifications caused by several forms of musculoskeletal complaints and risk factors such as low back pain and manual material handling (Wiktorin et al. 1993), neck-shoulder complaints and awkward postures of head, back and arms (Hansson et al. 2001), or upper limb complaints, and physical activity (Balogh et al. 2004). In terms of occupational kneeling or squatting, only a few studies considered the impact of musculoskeletal disorders on the assessment behaviour. Moreover, if complaints were taken into account, it was not about knee complaints. Burdorf and Laan (1991) found no impact of low back pain or shoulder pain on self-reported kneeling or squatting of mechanical repairmen.