This Article Full Text (OnlineFirst PDF) All Versions of this Article: 1756285609103726v1 2/4/205    most recent Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Add to Saved Citations Download to citation manager Request Permissions Request Reprints Add to My Marked Citations Citing Articles Citing Articles via Google Scholar Citing Articles via Scopus Google Scholar Articles by Hagell, P. Articles by Nilsson, M. H Search for Related Content Social Bookmarking                         What's this?

The 39-item Parkinson's disease questionnaire (PDQ-39): is it a unidimensional construct?

Lund University

^* To whom correspondence should be addressed. E-mail: Peter.Hagell{at}med.lu.se.

	Abstract

The 39-item Parkinson's Disease Questionnaire, and particularly its summary index (PDQ-39SI) is a widely used patient-reported clinical trial endpoint. A basic assumption when summing items into a total score is that they represent a common variable. We therefore assessed the unidimensionality of the PDQ-39SI using Rasch and confirmatory factor analysis. Both analyses showed model misfit. Adjustment for differential item functioning and disordered response category thresholds did not improve model fit, and residual analyses showed deviation from unidimensionality. These data indicate multidimensionality and challenge the interpretation and validity of PDQ-39SI scores. Clinicians and investigators should use and interpret the PDQ-39SI with caution.

First published on May 28, 2009, doi:10.1177/1756285609103726

Therapeutic Advances in Neurological Disorders 2009;2:205.

A more recent version of this article appeared on July 1, 2009


CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    Twitter    What's this?