[Psychometric attributes of the Parkinson's Disease-Cognitive Rating Scale. An independent validation study]

To perform an independent evaluation of the psychometric attributes of the Parkinson's Disease-Cognitive Rating Scale (PD-CRS).

The study involved patients with Parkinson's disease (PD) free of any impediments preventing them from participating in the required evaluation. Sociodemographic and historical data were collected for use in this observational, cross-sectional study and the following evaluations were employed: Scales for Outcomes in Parkinson's Disease-Motor Scale (SCOPA-Motor), Hoehn and Yahr staging (HY), Clinical Impression of Severity Index for Parkinson's Disease (CISI-PD), Minimental State Examination (MMSE), SCOPA-Cognitive (SCOPA-Cog), Non-Motor Symptoms Questionnaire and PD-CRS. Acceptability, internal consistence, construct validity and precision of the PD-CRS were analysed.

The sample consisted of 50 patients, with a mean age of 63.6 +/- 9.3 years. In all, 66% were males, with a history of 9 +/- 5.7 years with PD, in HY stages 1 to 4. Twelve patients (24%) presented data suggestive of dementia. The PD-CRS score was: sub-cortical sub-scale: 60.9 +/- 16.5; cortical sub-scale: 27.9 +/- 4.4; and total PD-CRS: 88.7 +/- 19.8. The mean-median difference was < 10% of the maximum scores and the total score showed no ceiling or floor effect. Cronbach's alpha was 0.85; the item-total correlations ranged from 0.57 (naming) to 0.73 (working memory), and the homogeneity index of the items was 0.36. Correlation with the MMSE and the SCOPA-Cog was high (rS = 0.53 and 0.77). The PD-CRS score was significantly lower in patients with a low level of schooling and more severe PD according to levels on the CISI-PD and distinguished between patients with and without dementia (70.3 +/- 26.2 versus 94.5 +/- 13; p < 0.001. The standard error of the measurement was 1.98.

The levels of acceptability, internal consistence, construct validity and precision displayed by the PD-CRS were satisfactory.