Blinded trial
Keeping patients (single-blind) or patients and doctors (double-blind) from knowing who is on which treatment, so that hopes and expectations cannot colour the results.
Blinding protects outcomes that involve judgement: how a patient rates their symptoms, whether a doctor decides a scan shows progression, or when to stop treatment; hard outcomes such as death are less vulnerable. Many cancer trials are open-label because the treatments are too different to disguise (an infusion versus a tablet, distinctive side effects), and they compensate by having scans read by a blinded independent central review (BICR) and by using overall survival, which cannot be biased by knowing the assignment. Unblinding a trial early, for example at an interim analysis, is a formal step overseen by an independent data monitoring committee.