title: Cross-sectional examination of musculoskeletal conditions and multimorbidity: influence of different thresholds and definitions on prevalence and association estimates.
abstract: BACKGROUND
  Multimorbidity and musculoskeletal conditions create substantial burden for people and health systems. Quantifying the extent of co-occurring conditions is hampered by conceptual heterogeneity, imprecision and/or indecision about how multimorbidity is defined. The purpose of this study is to examine the influence of different ways of operationalising multimorbidity on multimorbidity prevalence rates with a focus on working-age adults with musculoskeletal conditions. Weighted population prevalence rates of multimorbidity among working-age Australians were estimated using data from the National Health Survey. Two nominal thresholds (2+ or 3+ co-occurring conditions) and three operational definitions of multimorbidity (survey-, policy- and research-based) were examined. Using logistic regression, we estimated the association between the prevalence of multimorbidity among persons with musculoskeletal conditions compared to persons with non-musculoskeletal conditions for each definition and threshold combination.
  
  
  RESULTS
  As few as 7.9% of working-age Australians have 2+ conditions using the research-based definition (95% CI 7.4-8.5%), compared to estimates of 15.3% (95% CI 14.3-16.2%) and 61.5% (95% CI 60.3-62.7%). with the policy- and survey-based definitions, respectively. Depending on definition, with the 3+ threshold multimorbidity prevalence ranged from 2.1% (research) to 41.9% (survey). Among the sub-sample with musculoskeletal conditions, multimorbidity with the 2+ threshold ranged from 20.2 to 92.2%; and with 3+ threshold from 5.9 to 75.4%, again lowest with the research-definition and highest with the survey-definition. When compared to any other condition (i.e. non-musculoskeletal conditions), all musculoskeletal conditions were positively associated with multimorbidity, regardless of definition or threshold.
  
  
  CONCLUSIONS
  Depending on definition and threshold, multimorbidity is either rare or endemic in working-age Australians. Irrespective of definition, musculoskeletal conditions are a near-ubiquitous feature of multimorbidity.
authors.affiliation: Centre for Health Communication and Participation, School of Psychology and Public Health, College of Science, Health and Engineering, La Trobe University, Melbourne, Australia. d.lowe@latrobe.edu.au.|Cochrane Consumers and Communication Review Group, School of Psychology and Public Health, College of Science, Health and Engineering, La Trobe University, Melbourne, Australia. d.lowe@latrobe.edu.au.
authors.forename: Dianne B
authors.initials: DB
authors.lastname: Lowe
authors.affiliation: School of Allied Health, Australian Catholic University, Fitzroy, Australia.|Cochrane Consumers and Communication Review Group, School of Psychology and Public Health, College of Science, Health and Engineering, La Trobe University, Melbourne, Australia.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Taylor
authors.affiliation: Centre for Health Communication and Participation, School of Psychology and Public Health, College of Science, Health and Engineering, La Trobe University, Melbourne, Australia.|Cochrane Consumers and Communication Review Group, School of Psychology and Public Health, College of Science, Health and Engineering, La Trobe University, Melbourne, Australia.
authors.forename: Sophie J
authors.initials: SJ
authors.lastname: Hill
mesh_terms: D000293:Adolescent; D000328:Adult; D001315:Australia; D002908:Chronic Disease; D015897:Comorbidity; D003430:Cross-Sectional Studies; D005260:Female; D006291:Health Policy; D006801:Humans; D008297:Male; D008875:Middle Aged; D009140:Musculoskeletal Diseases / Q000150:complications* / Q000453:epidemiology*; D015995:Prevalence; D012044:Regression Analysis; D055815:Young Adult
keywords: Comorbidity; Multimorbidity; Musculoskeletal conditions; Prevalence