Abstract #302311

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JSM 2003 Abstract #302311
Activity Number: 299
Type: Contributed
Date/Time: Tuesday, August 5, 2003 : 2:00 PM to 3:50 PM
Sponsor: Biometrics Section
Abstract - #302311
Title: Agreement between Two Ratings with Different Ordinal Scales
Author(s): Sundar Natarajan*+ and Stuart Lipsitz and Neil S. Klar
Companies: New York University and Medical University of South Carolina and Cancer Care Ontario
Address: 423 East 23rd St., New York, NY, 10010-5013,
Keywords: Kappa ; cross-validation ; 2x2 tables
Abstract:

Agreement studies, where different observers rate the same subject on an ordinal scale, provide important information. The weighted Kappa coefficient is a popular measure of agreement for ordinal ratings. However, in some studies, the raters use scales with different numbers of categories. For example, a patient quality of life questionnaire may ask "How do you feel today?" with possible answers ranging from 1 (worst) to 7 (best). At the same visit, the doctor reports his view of the patient's health status as very poor, poor, fair, good, or very good. The weighted kappa coefficient is not applicable here since the two scales have different number of categories. We will discuss Kappa coefficients to measure agreement when there are R categories of one rating, and S categories of another. By dichotomizing the two ratings at all possible cutpoints, there are R(R-1)S(S-1)/4 possible (2 x 2) tables. For each of these (2 x 2) tables, we will estimate the Kappa coefficient for dichotomous ratings. The largest estimated Kappa coefficients will tell us the cutpoints for the two ratings where agreement is the best. Cross-validation will be used to evaluate the method.

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