Objective: The aim of the present study was to examine the validity and potential biases in self-reports of computer, mouse, and keyboard usage times, compared to objective recordings. Methods: A study population including 1211 persons was asked in a questionnaire to estimate the average time they had worked with computer, mouse, and keyboard during the past 4 working weeks. During the same period, a software program recorded these activities objectively. The study was part of a 1-year follow-up study from 2000 to 2001 of musculoskeletal outcomes among Danish computer workers. Results: Self-reports on computer, mouse and keyboard usage times were positively associated with objectively measured activity, but the validity was low. Self-reports explained only between a quarter and a third of the variance of objectively measured activity, and was even lower for one measure (keyboard time). Self-reports overestimated usage times. Overestimation was large at low levels and declined with increasing levels of objectively measured activity. Mouse usage time proportion was an exception with a near 1:1 relationship. Variability in objectively measured activity, arm pain, gender, and age influenced self-reports in a systematic way, but the effects were modest and sometimes in different directions. Conclusion: Self-reported durations of computer activities are positively associated with objective measures but they are quite inaccurate. Studies using self-reports to establish relations between computer work times and musculoskeletal pain could be biased and lead to falsely increased or decreased risk estimates.
- Activity monitoring
- Computer work
- Exposure assessment
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