What contributes to quality of life in patients with Parkinson's disease?

The question posed by Schrag et al 1(this issue, pp 308–312) is fundamental, but can it be answered? Quality of life belongs to a family of terms which has an improbably wide range of applications, from “quality” as an object of philosophical contemplation2 to “QoL” as an economic variable.3 It must be borne in mind that measures such as the PDQ-39 and the SF-36 differ considerably in content. More detail on the parallelism between the PDQ-39 and two other measures would be helpful but the data seem to support the assumption, which is gaining ground in the literature, that such measures reflect a single underlying dimension. Scales …