Parkinson's disease (PD) is a common neurodegenerative disease, affecting approximately 1.8% of the population over the age of 65. The prevalence of PD increases with age; it rises to 2.6% of the population between 85-89 years of age. The main clinical features of PD are motor symptoms such as, bradykinesia, rigidity, resting tremor and postural instability.

For a long time the main clinical focus in PD has been on the motor features, however, there is increasing recognition that the clinical spectrum of PD is more extensive, also including non-motor features such as cognitive dysfunction, depression, sleep disturbances, autonomic disturbances, pain, and motor and psychiatric complications of therapy. Furthermore, within the PD population, there is marked clinical heterogeneity, which may suggest that subgroups of PD exist that not only differ in the presence and severity of different impairments, but may also vary with respect to the rate of disease progression. Awareness of the whole spectrum of PD may improve if a conceptual model that describes the different levels of PD is used.

        The first phase of this study, the SCOPA project (SCales for Outcomes in PArkinson's disease) encompassed the construction of a disease-specific model of the disablement process, encompassing all relevant domains in PD on the levels of impairments, disabilities, global outcomes and intra and extra-individual factors that act on this pathway. The aim was then to select or develop an assessment scale for each PD domain. Prerequisites for the assessment scales were good reliability, validity, and (potential) responsiveness. Additional requirements for the assessment scales were that they were: (1) short, (2) practical, not requiring sophisticated measurement instruments, and (3) either self-assessed or could be used by research personnel without demanding extensive training.

        The second phase of this study, the SCOPA-PROPARK project (PROPARK: PROfiling PARKinson's disease) is a longitudinal study in which a large cohort of patients with Parkinson's disease (N=400) is evaluated annually with the complete SCOPA-assessment battery. The aim of this study is to describe the disablement process in PD over time and try to identify subgroups of PD patients.