Efficacy: can the intervention work?
Effectiveness: does the intervention work when used in normal practice?
Well resourced, 'ideal' setting
Highly selected; poorly adherent participants and those with conditions which might dilute the effect are often excluded
Little or no selection beyond the clinical indication of interest
Strictly enforced and adherence is monitored closely
Applied flexibly as it would be in normal practice
Often short-term surrogates, or process measures
Directly relevant to participants, funders, communities and healthcare practitioners
Relevance to practice
Indirect: little effort is made to match the design of the trial to the decision making needs of those in the usual setting in which the intervention will be implemented
Direct: the trial is designed to meet the needs of those making decisions about treatment options in the setting in which the intervention will be implemented