Interrater reliability of a clinical scale of rigidity

The purposes of this study were 1) to describe a clinical scale of rigidity and testing procedure for use in patients with Parkinson's disease and 2) to examine the scale's interrater reliability. Twenty subjects (3 women, 17 men; X̄ age = 64 years, s = 16.3) participated in the study. Criteria for participation were 1) diagnosis of Parkinson's disease, 2) physician-documented rigidity, 3) ability to follow one-step verbal directions, and 4) ability to attain at least 75% of the standard passive-range-of-motion measurements of the elbow, forearm, and wrist of the tested upper extremity. Each of two raters used a standardized set of instructions and test procedures. The degree of rigidity was assessed using a four-point scale ranging from 0 (absent) to 3 (severe). The observed agreement between raters was 16 out of 20 trials. A Cohen's weighted Kappa was used to analyze the data (Kw = .636, p = .20). Factors were identified that may have contributed to the discrepancy between agreement and the agreement beyond chance.