Validation and cross-cultural adaptation of the Self-Assessment Disability Scale in patients with Parkinson's disease in Serbia.

The symptoms of Parkinson's disease (PD) worsen over time affecting performance and causing disability. The purpose of this study was to translate the Self-Assessment Disability Scale in patients with Parkinson's disease (SADS-PD) into the Serbian language and assess its validity and reliability. From January to July 2012, 114 consecutive PD patients were recruited at the Neurology Clinic in Belgrade. The inclusion criteria were: ability to walk independently for at least 10 m, ability to stand for at least 90 s. The exclusion criteria were: cognitive impairment, the presence of other major neurologic, psychiatric, visual, audio-vestibular, and orthopedic disturbances. The 25-item SADS-PD was translated according to internationally-accepted methodology. The internal consistency of the scale was evaluated using Cronbach's alpha coefficient. Test-retest reliability was evaluated using Kendall's concordance coefficient for total scores. To evaluate construct validity, an exploratory factor analysis (principal component analysis, varimax rotation) was performed. Cronbach's alpha coefficient was 0.984. Kendall's concordance coefficient was 0.994. Duration of the disease, Hoehn & Yahr (H&Y) stage, Unified Parkinson's Disease Rating Scale (UPDRS) motor score, history of falls, Hamilton's Depression and Anxiety Rating Scales (HDRS and HARS) scores were significantly correlated with the total SADS-PD score. On factor analysis 25 items in the SADS-PD questionnaire were separated in two clusters with total matrix variance of 79.7 %. The psychometric properties of the cross-culturally adapted SADS-PD questionnaire (Serbian version) have outstanding validity and reliability as an instrument for evaluation of the extent of disability in patients with PD.