Use of Rasch analysis to refine a patient-reported questionnaire on satisfaction with communication of the multiple sclerosis diagnosis

Background: The Comunicazione medico-paziente nella Sclerosi Multipla Revised (COSM-R) is a patient self-assessed questionnaire probing the moment of multiple sclerosis (MS) diagnosis disclosure (section 1, five items) and following period (section 2, 15 items). Objectives: This study examined COSM-R dimensionality and measurement properties through Rasch analysis (partialcredit model) and proposed a revised questionnaire. Methods: Cross-sectional COSM-R data were obtained from 1068 people with MS (PwMS, 1065 questionnaires) articipating in four studies (102 centres). Mean age was 40 years (range 1773); 70% were women; 53% were from orthern, 25% from Central, and 21% from Southern Italy. esults: Unidimensionality was not confirmed for COSM-R section 1, but was for section 2 after removal of three tems. The revised instrument (COSM-S, Shortened) consisted of the original five-item checklist (section 1), modified by emoving the table grouping of three items, and 12 of the original 15 section 2 items, which could now be summed and ransformed into an interval scale. Scores were higher for items assessing emotional satisfaction than for those assessing nformational satisfaction. onclusions: The proposed COSM-S is a composite measure of satisfaction with MS diagnosis communication withimproved metric properties over the original COSM-R, and whose section 2 satisfies Rasch moel expectations.