The efficacy of a new cancer regimen is usually assessed by analyzing outcomes such as tumor response and overall survival. Many publications summarizing results of cancer clinical trials report measures such as odds ratios and hazard ratios, as these are the estimators of treatment effect obtained from regression models used to analyze the data.However, these measures are sometimes misinterpreted, as they are not necessarily familiar to many readers. The most common mistake is to interpret both measures as relative risks, an interpretation that can lead to an incorrect impression of the impact of the treatment on response and survival. The Oncologist 2002;7:181-187 The Medicine, Medical Center Boulevard, Winston-Salem, North Carolina 27157, USA. Telephone: 336-716-1048; Fax: 336-716-5425; e-mail: dcase@wfubmc.edu Received January 25, 2002; accepted for publication March 1, 2002. ©AlphaMed Press 1083-7159/2002
INTRODUCTIONThe effectiveness of a new agent or combination therapy in a prospective cancer clinical trial is usually assessed by analyzing outcomes such as tumor response and overall survival. Due to the widespread use of regression techniques for analyzing these outcomes, many publications summarizing results of cancer trials report measures of treatment effect such as odds ratios (ORs) and hazard ratios (HRs). Logistic regression, used to analyze tumor response, and Cox's proportional hazards regression, used to analyze censored survival data, give rise to the OR and HR, respectively, as measures of treatment effect. These are not necessarily familiar concepts to many readers, and they are sometimes misinterpreted. The tendency is to interpret both of these measures as relative risks (RRs), a more natural measure of effect in prospective clinical trials. For example, a doubling of the odds might be interpreted as a doubling in response or a 30% decrease in the hazard might be interpreted as a 30% improvement in 1-year or 5-year survival, both of which are incorrect interpretations. This misunderstanding is due partly to lack of training and