THE PDQ-8 - DEVELOPMENT AND VALIDATION OF A SHORT-FORM PARKINSONS-DISEASE QUESTIONNAIRE

The Parkinson's Disease Questionnaire (PDQ-39) is a disease specific m easure of health status which covers eight dimensions of ill-health, a nd contains 39 questions. The development of the questionnaire has bee n outlined in full elsewhere and is briefly outlined in this paper. Ps ychometric techniques are used here to derive a single index figure fr om the PDQ-39, transformed to a score range from 0 (good health) to 10 0 (poor health). A sub-set of items is then selected from the PDQ-39 t o create a shorter form version, the PDQ-8. Each item selected is the one most highly correlated with the overall domain score to which it c ontributes: in cases where more than one item correlated equally stron gly with the total then the item which received the highest completion rate was selected. The items were summed together and transformed ont o a score from 0 to 100. The results gained from the single index gain ed from the PDQ-39 are compared with that gained from the PDQ-8, and a re found to be remarkably similar. The use of the PDQ-8 is recommended over the PDQ-39 where a shorter form measure is required and where a single index measure of overall health status is acceptable or desirab le.