BACKGROUND: The Scale for Outcomes in Parkinson's disease (PD) for Autonomic Symptoms (SCOPA-AUT) is a specific scale to assess autonomic dysfunction in PD patients. It was developed and validated under the classic test theory approach. This study sought to test whether the SCOPA-AUT meets item response theory standards for reliability, internal construct validity, response category ordering, and differential item functioning by gender and age group. METHOD: The Rasch measurement model was applied to a sample of 385 PD patients. RESULTS: Model fit was obtained after the response categories were rescored and item 10-Incomplete emptying deleted because of redundancy. Person separation index, a reliability measure, was 0.82. All but two items (2-Sialorrhea and 13-Nocturia) were free of gender- and age-related bias. The strict tests of unidimensionality were met, indicating the validity of the total sumscore. Scale targeting suggested the need for items representing milder autonomic symptoms. CONCLUSIONS: Suggestions for improving the SCOPA-AUT include a shorter scale with a simpler response scheme and a combination of sexual items for men and women. The resulting SCOPA-AUT is a reliable scale, with good internal construct validity, providing Rasch transformed results on a linear metric scale.
BACKGROUND: The Scale for Outcomes in Parkinson's disease (PD) for Autonomic Symptoms (SCOPA-AUT) is a specific scale to assess autonomic dysfunction in PDpatients. It was developed and validated under the classic test theory approach. This study sought to test whether the SCOPA-AUT meets item response theory standards for reliability, internal construct validity, response category ordering, and differential item functioning by gender and age group. METHOD: The Rasch measurement model was applied to a sample of 385 PDpatients. RESULTS: Model fit was obtained after the response categories were rescored and item 10-Incomplete emptying deleted because of redundancy. Person separation index, a reliability measure, was 0.82. All but two items (2-Sialorrhea and 13-Nocturia) were free of gender- and age-related bias. The strict tests of unidimensionality were met, indicating the validity of the total sumscore. Scale targeting suggested the need for items representing milder autonomic symptoms. CONCLUSIONS: Suggestions for improving the SCOPA-AUT include a shorter scale with a simpler response scheme and a combination of sexual items for men and women. The resulting SCOPA-AUT is a reliable scale, with good internal construct validity, providing Rasch transformed results on a linear metric scale.
Authors: Anne Damian; Charles H Adler; Joseph G Hentz; Holly A Shill; John N Caviness; Marwan N Sabbagh; Virgilio G H Evidente; Thomas G Beach; Erika Driver-Dunckley Journal: Parkinsonism Relat Disord Date: 2012-07-06 Impact factor: 4.891
Authors: Anne Pavy-Le Traon; Nikki Cotterill; Gerard Amarenco; Susanne Duerr; Horacio Kaufmann; Heinz Lahrmann; François Tison; Gregor K Wenning; Christopher G Goetz; Werner Poewe; Cristina Sampaio; Anette Schrag; Olivier Rascol; Pablo Martinez-Martin; Glenn T Stebbins Journal: Mov Disord Clin Pract Date: 2018-10-25