title: Validity of questionnaire self-reports on computer, mouse and keyboard usage during a four-week period.
abstract: 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.
  
  
  CONCLUSIONS
  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.
authors: Department of Occupational Medicine, Copenhagen University Hospital, Glostrup, Denmark. simi@glostruphosp.kbhamt.dk
authors: Sigurd
authors: S
authors: Mikkelsen
authors: Imogen
authors: I
authors: Vilstrup
authors: Christina Funch
authors: CF
authors: Lassen
authors: Ann Isabel
authors: AI
authors: Kryger
authors: Jane Frølund
authors: JF
authors: Thomsen
authors: Johan Hviid
authors: JH
authors: Andersen
mesh_terms: D000328:Adult; D001132:Arm; D003201:Computers; D006801:Humans; D009140:Musculoskeletal Diseases / Q000209:etiology*; D009333:Neck; D009784:Occupational Diseases / Q000209:etiology*; D012650:Self Disclosure; D011795:Surveys and Questionnaires / Q000592:standards*