Treatment effect bias in randomised controlled trials using surrogate outcomes: a preliminary cohort study analysis

Background Ideally, decisions on the value of health technologies should be based on evidence from well-conducted clinical trials that assess clinically important final patientrelevant outcomes, such as mortality or impaired quality of life. Pressure to reduce the delay in the availability of technologies to patients has led to an increased reliance on the use of surrogate outcomes [1]. A key tenant of surrogate outcomes is unbiased quantification of the predictive treatment effect on the final patient-relevant clinical outcomes. This study compares the treatment outcome of trials that use a surrogate versus a final patient-relevant primary outcome.