Affiliations: Discipline of Physiotherapy, School of Health Sciences
Faculty of Health, The University of Newcastle, Newcastle, N.S.W. 2308,
Australia | Centre for Clinical Epidemiology and Biostatistics,
School of Medical Practice and Population Health, Faculty of Health, The
University of Newcastle, David Maddison Clinical Sciences Building, Royal
Newcastle Hospital, Newcastle, N.S.W. 2308, Australia
Note: [] Address for correspondence: Peter Osmotherly, Discipline of
Physiotherapy, Box 24, Hunter Building, The University of Newcastle, Callaghan,
NSW 2308, Australia. Fax: +61 2 49217902; E-mail:
[email protected]
Abstract: Background: The healthy worker survival effect is a complex and
poorly controlled bias affecting occupational studies. Little is known about
its behaviour in samples of computer based workers. This descriptive study
examined the healthy worker effect in relation to muscle performance and neck
pain in call-centre operators. Methods: 28 call-centre workers were examined for postural
muscle performance. Neck pain was measured using a validated questionnaire.
Analysis was by multivariate regression of the cohort, stratified by years of
employment. Results: Analysis using the entire sample failed to display
any relationship between neck pain and muscle performance. Further examination
revealed survival/secondary selection within the sample, with pain and poor
muscle performance reduced after 6 years employment. Stratified analysis
demonstrated that deep flexor muscle performance and posture were statistically
significantly associated with neck pain. Each stratum explained a greater
percentage of the variance in questionnaire scores, increasing from 42.3% for
the entire sample to 95.1% for the 4 years employed subgroup. Conclusion: The healthy worker survival effect is demonstrable
in occupations with lower physical demands. It should be considered in analysis
since it may obscure causal associations. There is no single method for
controlling this bias and greater understanding of its components is
required.
