Investigation of the psychometric properties of the inclusion body myositis functional rating scale with rasch analysis.
INTRODUCTION
The Inclusion Body Myositis Functional Rating Scale (IBMRFS) is a 10-item clinician-rated ordinal scale developed for people with inclusion body myositis.


METHODS
Single observations of the IBMFRS were collected from 132 patients. After Rasch analysis, modifications were made to the scale to optimize fit to the Rasch model while maintaining clinical validity and utility.


RESULTS
The original IBMFRS did not fit the assumptions of the Rasch model because of multidimensionality of the scale. Items assessed local dependence, disordered step thresholds, and differential item functioning. Deconstructing the scale into upper limb (IBMFRS-UL) and lower limb (IBMFRS-LL) scales improved fit to the Rasch model. A 9-item scale with the swallowing item removed (IBMFRS-9) remained multidimensional but demonstrated the ability to discriminate patients along the severity continuum. IBMFRS-UL, IBMFRS-LL, and IBMFRS-9 scores were transformed to a 0-100 scale for comparability.


DISCUSSION
This analysis has led to the development of 3 optimized versions of the IBMFRS. Muscle Nerve 60: 161-168, 2019.
['Ramdharry|Gita|G|0000-0001-9344-0301', 'Morrow|Jasper|J|', 'Hudgens|Stacie|S|', 'Skorupinska|Iwona|I|', 'Gwathmey|Kelly|K|', 'Currence|Melissa|M|', 'Herbelin|Laura|L|', 'Jawdat|Omar|O|', 'Pasnoor|Mamatha|M|', 'Mcvey|April|A|', 'Barohn|Richard J|RJ|', 'Burns|Ted M|TM|', 'Dimachkie|Mazen M|MM|', 'Amato|Anthony A|AA|', 'Hanna|Michael G|MG|', 'Machado|Pedro M|PM|']
D000328:Adult D000368:Aged D000369:Aged, 80 and over D005260:Female D006801:Humans D035002:Lower Extremity D008297:Male D008875:Middle Aged D018979:Myositis, Inclusion Body D011594:Psychometrics D015203:Reproducibility of Results D012720:Severity of Illness Index D034941:Upper Extremity
psychometric inclusion body myositis Rasch analysis modern test theory outcome measurement