What questions can large, simple trials answer?

Large, simple trials can provide reliable evidence on the balance of risk and benefit of widely practicable treatments that have moderate effects on major clinical outcomes. Treatments for stroke will potentially be used extensively world-wide. Each year about 8,000,000 people have an acute stroke, with about 5,000,000 being ischaemic. Of these, perhaps 1,000,000 receive medical attention within the first few hours of stroke onset. If reliable decisions about the treatment of such large numbers of patients are to be made, we need to be certain about the effects of treatment on death from any cause (and on other important outcomes) and in many different types of patient. Generally, such reliable evidence on whether to treat and on whom to treat, will only come from large, randomised trials recruiting many thousands of patients. Such trials are only feasible and affordable if they are simple.