title: Underemployment and mental health: comparing fixed-effects and random-effects regression approaches in an Australian working population cohort.
abstract: 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?
  
  
  
  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 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).
  
  
  
  We suggest underemployment to be a target of future workplace prevention strategies.
authors.affiliation: Centre for Health Equity, Melbourne School of Population and Global Health, The University of Melbourne, Melbourne, Victoria, Australia.|Work, Health and Wellbeing Unit, Centre for Population Health Research, School of Health and Social Development, Deakin University, Melbourne, Victoria, Australia.
authors.forename: Allison
authors.initials: A
authors.lastname: Milner
authors.affiliation: Centre for Health Equity, Melbourne School of Population and Global Health, The University of Melbourne, Melbourne, Victoria, Australia.|Work, Health and Wellbeing Unit, Centre for Population Health Research, School of Health and Social Development, Deakin University, Melbourne, Victoria, Australia.
authors.forename: Anthony D
authors.identifier: 0000-0002-5811-5906
authors.initials: AD
authors.lastname: LaMontagne
mesh_terms: D000328:Adult; D001315:Australia; D015331:Cohort Studies; D004651:Employment / Q000523:psychology*; D005260:Female; D006801:Humans; D008297:Male; D008603:Mental Health; D008875:Middle Aged; D011569:Psychiatric Status Rating Scales; D012044:Regression Analysis; D017678:Sex Distribution; D013997:Time Factors; D017132:Workplace / Q000523:psychology*
keywords: Underemployment; cohort; fixed-effects regression; longitudinal