title: A proposed method to investigate reliability throughout a questionnaire.
abstract: BACKGROUND
  Questionnaires are used extensively in medical and health care research and depend on validity and reliability. However, participants may differ in interest and awareness throughout long questionnaires, which can affect reliability of their answers. A method is proposed for "screening" of systematic change in random error, which could assess changed reliability of answers.
  
  
  METHODS
  A simulation study was conducted to explore whether systematic change in reliability, expressed as changed random error, could be assessed using unsupervised classification of subjects by cluster analysis (CA) and estimation of intraclass correlation coefficient (ICC). The method was also applied on a clinical dataset from 753 cardiac patients using the Jalowiec Coping Scale.
  
  
  RESULTS
  The simulation study showed a relationship between the systematic change in random error throughout a questionnaire and the slope between the estimated ICC for subjects classified by CA and successive items in a questionnaire. This slope was proposed as an awareness measure--to assessing if respondents provide only a random answer or one based on a substantial cognitive effort. Scales from different factor structures of Jalowiec Coping Scale had different effect on this awareness measure.
  
  
  CONCLUSIONS
  Even though assumptions in the simulation study might be limited compared to real datasets, the approach is promising for assessing systematic change in reliability throughout long questionnaires. Results from a clinical dataset indicated that the awareness measure differed between scales.
authors.affiliation: Unit of Biostatistics and Epidemiology, Oslo University Hospital, Kirkeveien 116, Oslo, Norway.
authors.forename: Tore
authors.initials: T
authors.lastname: Wentzel-Larsen
authors.forename: Tone M
authors.initials: TM
authors.lastname: Norekvål
authors.forename: Bjørg
authors.initials: B
authors.lastname: Ulvik
authors.forename: Ottar
authors.initials: O
authors.lastname: Nygård
authors.forename: Are H
authors.initials: AH
authors.lastname: Pripp
mesh_terms: D000465:Algorithms; D002318:Cardiovascular Diseases / Q000523:psychology; D016000:Cluster Analysis; D003198:Computer Simulation; D006801:Humans; D016014:Linear Models; D015203:Reproducibility of Results; D055500:Resilience, Psychological; D011795:Surveys and Questionnaires / Q000592:standards