title: Item response theory and factor analysis as a mean to characterize occurrence of response shift in a longitudinal quality of life study in breast cancer patients.
abstract: BACKGROUND
  The occurrence of response shift (RS) in longitudinal health-related quality of life (HRQoL) studies, reflecting patient adaptation to disease, has already been demonstrated. Several methods have been developed to detect the three different types of response shift (RS), i.e. recalibration RS, 2) reprioritization RS, and 3) reconceptualization RS. We investigated two complementary methods that characterize the occurrence of RS: factor analysis, comprising Principal Component Analysis (PCA) and Multiple Correspondence Analysis (MCA), and a method of Item Response Theory (IRT).
  
  
  METHODS
  Breast cancer patients (n = 381) completed the EORTC QLQ-C30 and EORTC QLQ-BR23 questionnaires at baseline, immediately following surgery, and three and six months after surgery, according to the "then-test/post-test" design. Recalibration was explored using MCA and a model of IRT, called the Linear Logistic Model with Relaxed Assumptions (LLRA) using the then-test method. Principal Component Analysis (PCA) was used to explore reconceptualization and reprioritization.
  
  
  RESULTS
  MCA highlighted the main profiles of recalibration: patients with high HRQoL level report a slightly worse HRQoL level retrospectively and vice versa. The LLRA model indicated a downward or upward recalibration for each dimension. At six months, the recalibration effect was statistically significant for 11/22 dimensions of the QLQ-C30 and BR23 according to the LLRA model (p ≤ 0.001). Regarding the QLQ-C30, PCA indicated a reprioritization of symptom scales and reconceptualization via an increased correlation between functional scales.
  
  
  CONCLUSIONS
  Our findings demonstrate the usefulness of these analyses in characterizing the occurrence of RS. MCA and IRT model had convergent results with then-test method to characterize recalibration component of RS. PCA is an indirect method in investigating the reprioritization and reconceptualization components of RS.
authors.affiliation: Quality of Life in Oncology Platform, Besançon, France. aanota@chu-besancon.fr.
authors.forename: Amélie
authors.initials: A
authors.lastname: Anota
authors.forename: Caroline
authors.initials: C
authors.lastname: Bascoul-Mollevi
authors.forename: Thierry
authors.initials: T
authors.lastname: Conroy
authors.forename: Francis
authors.initials: F
authors.lastname: Guillemin
authors.forename: Michel
authors.initials: M
authors.lastname: Velten
authors.forename: Damien
authors.initials: D
authors.lastname: Jolly
authors.forename: Mariette
authors.initials: M
authors.lastname: Mercier
authors.forename: Sylvain
authors.initials: S
authors.lastname: Causeret
authors.forename: Jean
authors.initials: J
authors.lastname: Cuisenier
authors.forename: Olivier
authors.initials: O
authors.lastname: Graesslin
authors.forename: Zeinab
authors.initials: Z
authors.lastname: Hamidou
authors.forename: Franck
authors.initials: F
authors.lastname: Bonnetain
mesh_terms: D001294:Attitude to Health; D001943:Breast Neoplasms / Q000523:psychology* / Q000601:surgery / Q000628:therapy; D005163:Factor Analysis, Statistical; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008408:Mastectomy / Q000523:psychology; D008875:Middle Aged; D025341:Principal Component Analysis; D011594:Psychometrics; D011788:Quality of Life / Q000523:psychology*; D011795:Surveys and Questionnaires