title: Somatic symptom reports in the general population: Application of a bi-factor model to the analysis of change.
abstract: OBJECTIVE
  To investigate the latent structure of somatic symptom reports in the general population with a bi-factor model and apply the structure to the analysis of change in reported symptoms after the emergence of an uncertain environmental health risk.
  
  
  METHODS
  Somatic symptoms were assessed in two general population environmental health cohorts (AMIGO, n=14,829 & POWER, n=951) using the somatization scale of the four-dimensional symptom questionnaire (4DSQ-S). Exploratory bi-factor analysis was used to determine the factor structure in the AMIGO cohort. Multi-group and longitudinal models were applied to assess measurement invariance. For a subsample of residents living close to a newly introduced power line (n=224), we compared a uni- and multidimensional method for the analysis of change in reported symptoms after the power line was put into operation.
  
  
  RESULTS
  We found a good fit (RMSEA=0.03, CFI=0.98) for a bi-factor model with one general and three symptom specific factors (musculoskeletal, gastrointestinal, cardiopulmonary). The latent structure was found to be invariant between cohorts and over time. A significant increase (p<.05) was found only for musculoskeletal and gastrointestinal symptoms after the power line was put into operation.
  
  
  CONCLUSIONS
  In our study we found that a bi-factor structure of somatic symptoms reports was equivalent between cohorts and over time. Our findings suggest that taking this structure into account can lead to a more informative interpretation of a change in symptom reports compared to a unidimensional approach.
authors.affiliation: Department of Public and Occupational Health, EMGO Institute for Health and Care Research, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Jarry T
authors.initials: JT
authors.lastname: Porsius
authors.affiliation: Department of Public and Occupational Health, EMGO Institute for Health and Care Research, VU University Medical Center, Amsterdam, The Netherlands; Institute for Risk Assessment Sciences (IRAS), Division Environmental Epidemiology, Utrecht University, Yalelaan 2, 3584 CM Utrecht, The Netherlands. Electronic address: a.l.martens@uu.nl.
authors.forename: Astrid L
authors.initials: AL
authors.lastname: Martens
authors.affiliation: Department of Public and Occupational Health, EMGO Institute for Health and Care Research, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Pauline
authors.initials: P
authors.lastname: Slottje
authors.affiliation: Department of Public and Occupational Health, EMGO Institute for Health and Care Research, VU University Medical Center, Amsterdam, The Netherlands; National Institute for Public Health and the Environment (RIVM), Bilthoven, The Netherlands.
authors.forename: Liesbeth
authors.initials: L
authors.lastname: Claassen
authors.affiliation: Netherlands Institute for Health Services Research (NIVEL), The Netherlands.
authors.forename: Joke C
authors.initials: JC
authors.lastname: Korevaar
authors.affiliation: Department of Public and Occupational Health, EMGO Institute for Health and Care Research, VU University Medical Center, Amsterdam, The Netherlands; National Institute for Public Health and the Environment (RIVM), Bilthoven, The Netherlands.
authors.forename: Danielle R M
authors.initials: DR
authors.lastname: Timmermans
authors.affiliation: Institute for Risk Assessment Sciences (IRAS), Division Environmental Epidemiology, Utrecht University, Yalelaan 2, 3584 CM Utrecht, The Netherlands.
authors.forename: Roel
authors.initials: R
authors.lastname: Vermeulen
authors.affiliation: Department of Public and Occupational Health, EMGO Institute for Health and Care Research, VU University Medical Center, Amsterdam, The Netherlands; KLM Health Services, Schiphol, The Netherlands.
authors.forename: Tjabe
authors.initials: T
authors.lastname: Smid
mesh_terms: D000328:Adult; D000368:Aged; D015331:Cohort Studies; D004782:Environmental Health; D005163:Factor Analysis, Statistical; D005260:Female; D005767:Gastrointestinal Diseases / Q000453:epidemiology; D006331:Heart Diseases / Q000453:epidemiology; D006801:Humans; D008171:Lung Diseases / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D009140:Musculoskeletal Diseases / Q000453:epidemiology; D018570:Risk Assessment; D013001:Somatoform Disorders / Q000453:epidemiology* / Q000503:physiopathology; D011795:Surveys and Questionnaires
keywords: Bi-factor model; Latent structure; Measurement invariance; Self-report; Somatic symptoms; Symptom patterns