Evidence-based guidelines for using the Short Form 36 in cervical dystonia.

We aimed to provide evidence-based guidelines for using the Short Form 36 (SF-36) as an outcome measure in cervical dystonia (CD). To do this, we tested the hypothesized relationships between items, scales, and summary measures of the SF-36 using psychometric analyses in data from a postal survey of 235 people with CD. Although the majority of subscales performed adequately, the Role Physical and Role Emotional subscales had substantial floor and/or ceiling effects. Evidence did not support computing SF-36 Physical and Mental Component Summary scores. We propose guidelines that include the recommendation that these subscale and summary scores should be reported with caution.