title: Addressing challenges of validity and internal consistency of mental health measures in a 27- year longitudinal cohort study - the Northern Swedish Cohort study.
abstract: BACKGROUND
  There are inherent methodological challenges in the measurement of mental health problems in longitudinal research. There is constant development in definitions, taxonomies and demands concerning the properties of mental health measurements. The aim of this paper was to construct composite measures of mental health problems (according to today's standard) from single questionnaire items devised in the early 1980s, and to evaluate their internal consistency and factorial invariance across the life course using the Northern Swedish Cohort.
  
  
  METHODS
  All pupils in the last year of compulsory school in Luleå in 1981 (n = 1083) form a prospective cohort study where the participants have been followed with questionnaires from the age of 16 (in 1981) until the age of 43 (in 2008). We created and tested the following composite measures from self-reports at each follow-up: depressive symptoms, anxiety symptoms, functional somatic symptoms, modified GHQ and positive health. Validity and internal consistency were tested by confirmatory factor analysis, including tests of factorial invariance over time.
  
  
  RESULTS
  As an overall assessment, the results showed that the composite measures (based on more than 30-year-old single item questions) are likely to have acceptable factorial invariance as well as internal consistency over time.
  
  
  CONCLUSIONS
  Testing the properties of the mental health measures used in older studies according to the standards of today is of great importance in longitudinal research. Our study demonstrates that composite measures of mental health problems can be constructed from single items which are more than 30 years old and that these measures seem to have the same factorial structure and internal consistency across a significant part of the life course. Thus, it can be possible to overcome some specific inherent methodological challenges in using historical data in longitudinal research.
authors.affiliation: Department of Public Health and Clinical Medicine, Unit of Social Medicine, Umeå University, 901 85, Umeå, Sweden. anne.hammarstrom@umu.se.
authors.forename: Anne
authors.initials: A
authors.lastname: Hammarström
authors.affiliation: Stress Research Institute, Stockholm University, Stockholm, Sweden.
authors.forename: Hugo
authors.initials: H
authors.lastname: Westerlund
authors.affiliation: School of Social Sciences and Humanities, Psychology, University of Tampere, Tampere, Finland.|Finnish Institute of Occupational Health, Helsinki, Finland.
authors.forename: Kaisa
authors.initials: K
authors.lastname: Kirves
authors.affiliation: Department of Public Health and Clinical Medicine, Unit of Social Medicine, Umeå University, 901 85, Umeå, Sweden.
authors.forename: Karina
authors.initials: K
authors.lastname: Nygren
authors.affiliation: Department of Public Health and Clinical Medicine, Unit of Social Medicine, Umeå University, 901 85, Umeå, Sweden.|School of Health Sciences, University of Tampere, Tampere, Finland.
authors.forename: Pekka
authors.initials: P
authors.lastname: Virtanen
authors.affiliation: Department of Clinical Sciences, Division of Child and Adolescent Psychiatry, Umeå University, Umeå, Sweden.
authors.forename: Bruno
authors.initials: B
authors.lastname: Hägglöf
mesh_terms: D000293:Adolescent; D000328:Adult; D001007:Anxiety / Q000175:diagnosis* / Q000523:psychology; D016009:Chi-Square Distribution; D003863:Depression / Q000175:diagnosis* / Q000523:psychology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008603:Mental Health / Q000706:statistics & numerical data*; D011446:Prospective Studies; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012959:Socioeconomic Factors; D011795:Surveys and Questionnaires; D013548:Sweden; D055815:Young Adult