International use of health status questionnaires in Parkinson's disease: translation is not enough

The present study assessed the linguistic and content validity of the Swedish version of the 39-item Parkinson's disease questionnaire (PDQ-39). The frame question, response alternatives and two of the 39 items yielded substantial linguistic and stylistic problems. Such shortcomings would be expected to influence responses to, and the quality of, the whole questionnaire. Data support content validity of the PDQ-39 as a functional health status questionnaire, although some shortcomings were identified. This preliminary study illustrates the need for documented linguistic validity before new language adaptations of patient-reported outcome measures can be considered suitable for use in clinical trials, research, and practice.