> An ethical dilemma arises in a clinical trial when the investigator(s) begin to believe that the treatment or intervention administered in one arm of the trial is significantly outperforming the other arms. A trial should begin with a null hypothesis, and there should exist no decisive evidence that the intervention or drug being tested will be superior to existing treatments, or that it will be completely ineffective. As the trial progresses, the findings may provide sufficient evidence to convince the investigator of the intervention or drug's efficacy. Once a certain threshold of evidence is passed, there is no longer genuine uncertainty about the most beneficial treatment, so there is an ethical imperative for the investigator to provide the superior intervention to all participants.
> An ethical dilemma arises in a clinical trial when the investigator(s) begin to believe that the treatment or intervention administered in one arm of the trial is significantly outperforming the other arms. A trial should begin with a null hypothesis, and there should exist no decisive evidence that the intervention or drug being tested will be superior to existing treatments, or that it will be completely ineffective. As the trial progresses, the findings may provide sufficient evidence to convince the investigator of the intervention or drug's efficacy. Once a certain threshold of evidence is passed, there is no longer genuine uncertainty about the most beneficial treatment, so there is an ethical imperative for the investigator to provide the superior intervention to all participants.
> https://en.wikipedia.org/wiki/Clinical_equipoise