title: Development of a multimorbidity illness perceptions scale (MULTIPleS).
abstract: BACKGROUND
  Illness perceptions are beliefs about the cause, nature and management of illness, which enable patients to make sense of their conditions. These perceptions can predict adjustment and quality of life in patients with single conditions. However, multimorbidity (i.e. patients with multiple long-term conditions) is increasingly prevalent and a key challenge for future health care delivery. The objective of this research was to develop a valid and reliable measure of illness perceptions for multimorbid patients.
  
  
  METHODS
  Candidate items were derived from previous qualitative research with multimorbid patients. Questionnaires were posted to 1500 patients with two or more exemplar long-term conditions (depression, diabetes, osteoarthritis, coronary heart disease and chronic obstructive pulmonary disease). Data were analysed using factor analysis and Rasch analysis. Rasch analysis is a modern psychometric technique for deriving unidimensional and intervally-scaled questionnaires.
  
  
  RESULTS
  Questionnaires from 490 eligible patients (32.6% response) were returned. Exploratory factor analysis revealed five potential subscales 'Emotional representations', 'Treatment burden', 'Prioritising conditions', 'Causal links' and 'Activity limitations'. Rasch analysis led to further item reduction and the generation of a summary scale comprising of items from all scales. All scales were unidimensional and free from differential item functioning or local independence of items. All scales were reliable, but for each subscale there were a number of patients who scored at the floor of the scale.
  
  
  CONCLUSIONS
  The MULTIPleS measure consists of five individual subscales and a 22-item summary scale that measures the perceived impact of multimorbidity. All scales showed good fit to the Rasch model and preliminary evidence of reliability and validity. A number of patients scored at floor of each subscale, which may reflect variation in the perception of multimorbidity. The MULTIPleS measure will facilitate research into the impact of illness perceptions on adjustment, clinical outcomes, quality of life, and costs in patients with multimorbidity.
authors.affiliation: NIHR Collaboration for Leadership in Applied Health Research and Care for Greater Manchester, University of Manchester, Manchester, United Kingdom ; NIHR School for Primary Care Research, NIHR Greater Manchester Primary Care Patient Safety Translational Research Centre, Manchester Academic Health Science Centre (MAHSC), University of Manchester, Manchester, United Kingdom.
authors.forename: Chris J
authors.initials: CJ
authors.lastname: Gibbons
authors.affiliation: NIHR School for Primary Care Research, NIHR Greater Manchester Primary Care Patient Safety Translational Research Centre, Manchester Academic Health Science Centre (MAHSC), University of Manchester, Manchester, United Kingdom.
authors.forename: Cassandra
authors.initials: C
authors.lastname: Kenning
authors.affiliation: NIHR Collaboration for Leadership in Applied Health Research and Care for Greater Manchester, University of Manchester, Manchester, United Kingdom ; NIHR School for Primary Care Research, NIHR Greater Manchester Primary Care Patient Safety Translational Research Centre, Manchester Academic Health Science Centre (MAHSC), University of Manchester, Manchester, United Kingdom.
authors.forename: Peter A
authors.initials: PA
authors.lastname: Coventry
authors.affiliation: School of Nursing, Midwifery and Social Work, University of Manchester, Manchester, United Kingdom.
authors.forename: Penny
authors.initials: P
authors.lastname: Bee
authors.affiliation: Manchester Centre for Health Psychology, Institute of Inflammation and Repair, University of Manchester, Manchester, United Kingdom.
authors.forename: Christine
authors.initials: C
authors.lastname: Bundy
authors.affiliation: NIHR School for Primary Care Research, NIHR Greater Manchester Primary Care Patient Safety Translational Research Centre, Manchester Academic Health Science Centre (MAHSC), University of Manchester, Manchester, United Kingdom.
authors.forename: Louise
authors.initials: L
authors.lastname: Fisher
authors.affiliation: NIHR School for Primary Care Research, NIHR Greater Manchester Primary Care Patient Safety Translational Research Centre, Manchester Academic Health Science Centre (MAHSC), University of Manchester, Manchester, United Kingdom.
authors.forename: Peter
authors.initials: P
authors.lastname: Bower
mesh_terms: D015897:Comorbidity; D016638:Critical Illness; D003710:Demography; D005163:Factor Analysis, Statistical; D006801:Humans; D016015:Logistic Models; D009017:Morbidity; D049451:Nomograms; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires