Departments of Laboratory Medicine and Pharmacy, Schools of Medicine and Pharmacy, University of California San Francisco

Correspondence: Lewis B Sheiner, MD, room C-255, Box 0626, University of California San Francisco, San Francisco, C A 94143-0626.

Received 27 September 1993; Accepted 21 March 1994.

Abstract

A clinical trial of an analgesic agent compares pain relief scores (ordered categorical responses) over time among groups of patients, each subject to a painful procedure and given various doses of active agent (including zero, i.e., placebo) on demand. Patients may elect to remedicate with an active agent if their pain relief is insufficient, so the sample of patients at any given time is biased toward those with better relief. Standard analyses usually (1) fill in the missing data but make no correction for so doing and (2) treat the ordered categorical variable as continuous. Both of these create problems in interpretation and inference, but the former is more serious than the latter. An alternative analysis has been recently proposed that deals with these problems. This article presents that method for a nonstatistical audience and illustrates its use on some data from the analgesic bromfenac.