Megatrials are commonly used to establish small differences of new drugs over existing drugs, e.g. the global utilization of streptokinase and t-PA for occluded coronary arteries (GUSTO) study. Thus, they can be important marketing tools and can justify the use of the new and usually more expensive agents instead of older therapies of proven value (Hampton 1996).

Unlike conventional randomized clinical trials, megatrials do not usually attempt to control for confounding variables—rather, their goal is to distribute bias evenly between groups of subjects. The group, rather than the individual, is the subject of analysis. Megatrials appear to have had their biggest impact when used to compare different allocated protocols with respect to a selected outcome. These trials consist of large numbers of patients (up to tens of thousands) and typically have very loose entry criteria, although the ideal megatrial study population should be representative of the target population and have rigorous diagnostic criteria for entry (Charlton 1996).

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