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Commentary: methodological approaches to understanding mechanisms and ‘what if’ questions in occupational health research
  1. Peter M Smith1,2,3
  1. 1 Institute for Work & Health, Toronto, Ontario, Canada
  2. 2 Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada
  3. 3 Department of Epidemiology and Preventive Medicine, Monash University, Clayton, Victoria, Australia
  1. Correspondence to Dr Peter M Smith, Institute of Work & Health, Toronto, Ontario, Canada; psmith{at}

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In occupational health research investigators can often be interested in better understanding the factors that explain the relationship between an exposure and an outcome. Two recent examples of such papers published in Occupational and Environmental Medicine are from Shields and colleagues exploring the extent to which differences in employment between people living with and without a disability in Australia explain differences in mental health outcomes,1 and Siegrist and colleagues examining how psychosocial exposures at work interact with socioeconomic position to increase risk of non-fatal cardiovascular disease events.2 The paper by Shields et al 1 uses a potential outcomes approach to mediation, based on VanderWeele’s model based approach.3 This analytical approach is increasingly accessible to researchers with many statistical programmes now incorporating specific procedures for such analyses.4 In their paper, Shields and colleagues observe an overall effect (or total effect) of an approximately five-point difference in the mental health scores of between respondents who are living with a disability compared with those without a disability—which they note is socially relevant.1 Through their mediation approach they were further able to estimate that 19% of this total effect is via the employment pathway, while 81% is not.1

In the paper by Siegrist et al, despite psychosocial work exposures commonly being considered an outcome of one’s education and/or occupational position,5 a mediation approach is not taken. Rather, a series of discrete-time survival models are used to explore interaction, on both additive and multiplicative scales, between various measures of socioeconomic position and effort-reward imbalance (ERI). Siegrist and colleagues observed that while both measures of socioeconomic status and ERI are associated with an increased risk of cardiovascular disease events, there was no interaction between socioeconomic position and ERI. As stated in …

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  • Contributors PMS wrote the editorial.

  • Funding PMS works for the Institute for Work & Health (IWH). IWH is supported through funding from the Ontario's Ministry of Labour, Immigration, Training and Skills Development.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; internally peer reviewed.

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