• Back disorders
• occupational health practice
• ergonomics
• epidemiology
• neuropsychology

We appreciate the careful reading of our editorial1 by Drs Mikkelsen and Andersen.2 We regret our omission of the one published NUDATA study that was available at the time our editorial was submitted.3 That study reported significant associations between mouse usage time collected with memory resident software and both acute neck pain and acute shoulder pain among 2146 technical assistants. However, because (1) median mouse usage time was 5.2 h/week and median keyboard usage time was 0.9 h/week and (2) rates of moderate or greater musculoskeletal pain were very low among the participating computer users we are concerned about the generalisability of the observed associations to workers with greater mouse and keyboard use.

Regarding differences in associations with musculoskeletal disorders observed across studies using self-reported estimates of computer use versus memory resident software documentation of computer use we made no argument that one was correct and the other was incorrect. Rather, we raised the concern that these two exposure assessment methods capture different (but not totally unrelated) aspects of computer use relevant to musculoskeletal disorder risk. The absence of a perfect correlation between self-reported estimates of computer use and memory resident software documentation of computer use may be due to error in self-reporting, differences in the kind of exposure information captured or both. The claims of methodological objectivity and validity presented by Mikkelsen and Andersen do not address this fundamental question. We continue to believe, as noted in our editorial, that a better understanding of the attributes of work captured by self-report and by computer registration software will clarify what appear to be inconsistent results reported by studies using them.