ROC area discrimination (ROCAD) curve: a new method of evaluating the discriminating ability of ordinal scales.
OBJECTIVE
The area under the receiver operating characteristic (ROC) curve has been frequently used to assess the ability of diagnostic tests to discriminate between individuals with and without a disease. In this paper, we propose to use the ROC area to evaluate the discriminating power of ordinal measures, such as many subjective ratings or multioption questionnaire items.


METHODS
Applications of the method are illustrated with examples from a study designed to select multioption items for a quality-of-life questionnaire in persons with arthritis.


RESULTS
DISCRIMINATION was defined as the ability to discriminate between subjects above and below a given threshold value for the attribute being measured. The ROC curve for an ordinal scale was obtained for each observed value of the attribute and the areas under the ROC curves were estimated and plotted on a graph. The resultant curve is referred to as the ROC Area Discrimination (ROCAD) curve. In contrast to standard measures of validity for ordinal scales, such as a correlation coefficient, the ROCAD curve describes the performance of the scale for each point along the spectrum of the measured attribute.


CONCLUSIONS
ROCAD curves can be useful in evaluating the discriminating power of ordinal scales.
Kopec
Jacek A
JA
Department of Health Care and Epidemiology, University of British Columbia, Arthritis Research Centre of Canada, Vancouver, BC, Canada. jkopec@arthritisresearch.ca
Sayre
Eric C
EC
D000203:Activities of Daily Living; D001168:Arthritis / Q000534:rehabilitation; D003627:Data Interpretation, Statistical; D006801:Humans; D010147:Pain Measurement; D012372:ROC Curve; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires