A holistic approach to evaluating Parkinson’s disease, using the Delphi method: a linear evaluation index

BACKGROUND: Parkinson’s disease (PD) is a chronic disease that presents a multitude of symptoms, with symptoms of both motor and nonmotor nature. The Delphi method is widely used to create consensuses among experts in a field of knowledge. OBJECTIVE: In order to reach a consensus on the values that should be assigned to the different motor and nonmotor manifestations of Parkinson’s disease, a linear evaluation index (LEI) was created. Subsequently, the metric properties of this index were studied. METHODS: 120 consecutive patients with a Parkinson’s diagnosis were chosen in accordance with the UKPDSBB criteria. The Delphi method was used to reach a consensus among experts regarding the values of each of the manifestations included. Subsequently, the following attributes were analyzed: quality and acceptability of the data; reliability, in terms of internal consistency, reliability index, Cronbach’s alpha and standard error of measurement; and validity, in terms of convergent validity and validity for known groups. RESULTS: Twenty-five experts participated. The importance factor did not differ between the first round and the second round (chi-square test). We analyzed the responses that assigned percentage values to the 10 dimensions of the LEI. Both in the first and in the second round, the values of the scattering coefficient Vr were always close to 0. The homogeneity index was 0.36; the corrected-item total correlation values ranged from 0.02 to 0.7; Cronbach’s α was 0.69; and the SEM was 4.23 (55.1%). CONCLUSIONS: The LEI was obtained through rigorous recommended methodology. The results showed adequate metric properties.