AN APPLICATION OF BRADLEY-TERRY-TYPE MODELS TO THE MEASUREMENT OF PAIN

A case-study concerning the measurement of pain experienced in the adm inistration of routine subcutaneous injections to patients undergoing regular haemodialysis is presented. The four treatments studied had a 2 x 2 factorial structure: one factor comprised two forms of the anaem ia correcting substance erythropoietin, and the other whether an anaes thetic or placebo cream was applied to the injection site. On a visit to the dialysis unit, a patient is given two of the treatments, one in each arm, and asked to nominate the less painful injection; on a subs equent visit the patient is asked to compare the remaining treatments in a similar way. These paired comparisons are analysed by using a ver sion of the Bradley-Terry model which accommodates ties and order effe cts. Extensions to the method to allow for factorial treatments and de pendent judgments are developed.