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Underemployment and mental health: comparing fixed-effects and random-effects regression approaches in an Australian working population cohort
  1. Allison Milner1,2,
  2. Anthony D LaMontagne1,2
  1. 1Centre for Health Equity, Melbourne School of Population and Global Health, The University of Melbourne, Melbourne, Victoria, Australia
  2. 2Work, Health and Wellbeing Unit, Centre for Population Health Research, School of Health and Social Development, Deakin University, Melbourne, Victoria, Australia
  1. Correspondence to Dr Allison Milner, Centre for Health Equity, School of Population and Global Health, University of Melbourne, Melbourne, VIC 3010, Australia; allison.milner{at}


Objectives Underemployment occurs when workers are available for more hours of work than offered. It is a serious problem in many Organisation for Economic Co-operation and Development (OECD) countries, and particularly in Australia, where it affects about 8% of the employed population. This paper seeks to answer the question: does an increase in underemployment have an influence on mental health?

Methods The current paper uses data from an Australian cohort of working people (2001–2013) to investigate both within-person and between-person differences in mental health associated with being underemployed compared with being fully employed. The main exposure was underemployment (not underemployed, underemployed 1–5, 6–10, 11–20 and over 21 hours), and the outcome was the five-item Mental Health Inventory.

Results Results suggest that stepwise declines in mental health are associated with an increasing number of hours underemployed. Results were stronger in the random-effects (11–20 hours =−1.53, 95% CI −2.03 to −1.03, p<0.001; 21 hours and over −2.24, 95% CI −3.06 to −1.43, p<0.001) than fixed-effects models (11–20 hours =−1.11, 95% CI −1.63 to −0.58, p<0.001; 21 hours and over −1.19, 95% CI −2.06 to −0.32, p=0.008). This likely reflects the fact that certain workers were more likely to suffer the negative effects of underemployment than others (eg, women, younger workers, workers in lower-skilled jobs and who were casually employed).

Conclusions We suggest underemployment to be a target of future workplace prevention strategies.

  • Underemployment
  • cohort
  • longitudinal
  • fixed-effects regression

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  • Contributors AM and ADL designed the study. AM prepared the methods and results sections of the text. ADL contributed to the interpretation of results. AM wrote the discussion and the introduction, with contributions from ADL. All authors approved the final version of this manuscript and its previous drafts.

  • Funding This work is supported by a grant awarded to AM by beyondblue and the Movember foundation. Additional support was also provided by a Victorian Health Promotion Foundation Centre grant #15732.

  • Disclaimer The findings and views reported in this paper are those of the authors and should not be attributed to either DSS or the Melbourne Institute.

  • Competing interests None declared.

  • Ethics approval Department of Social Services.

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

  • Data sharing statement Data is available from the Melbourne Institute for approved users.