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Validity of questionnaire self-reports on computer, mouse and keyboard usage during a four-week period
  1. Sigurd Mikkelsen1,
  2. Imogen Vilstrup2,
  3. Christina Funch Lassen1,
  4. Ann Isabel Kryger1,
  5. Jane Frølund Thomsen1,
  6. Johan Hviid Andersen2
  1. 1Department of Occupational Medicine, Copenhagen University Hospital, Glostrup, Denmark
  2. 2Department of Occupational Medicine, Herning Hospital, Herning, Denmark
  1. Correspondence to:
 Dr S Mikkelsen
 Department of Occupational Medicine, Copenhagen University Hospital, Glostrup, Nordre Ringvej, DK 2600 Glostrup, Denmark; simi{at}


Objective: To examine the validity and potential biases in self-reports of computer, mouse and keyboard usage times, compared with objective recordings.

Methods: A study population of 1211 people was asked in a questionnaire to estimate the average time they had worked with computer, mouse and keyboard during the past four working weeks. During the same period, a software program recorded these activities objectively. The study was part of a one-year follow-up study from 2000–1 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 were 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 relation. 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.

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  • Published Online First 26 March 2007

  • Funding: Danish Medical Research Council; grant number 9801292, Danish Ministry of Employment, via National Work Environment Authority; grant number 20000010486.

  • Competing interests: None.