Why do research ethics committees disagree with each other?

Research ethics committees have to ensure that research projects are asking sensible questions and are designed so that the questions will be answered, that the research subjects who are involved will not come to unnecessary harm, and that the autonomy of the research subjects will be respected. Where research proposals cannot fulfill all these criteria, research ethics committees have to perform a delicate balancing act amongst competing moral claims. These arise when, for example, the research is non-therapeutic or the research subjects are incompetent to give consent. Given that the balance of conclusions is so sensitive, it is hardly surprising that different committees sometimes disagree with each other.