Pragmatic versus explanatory trials: effectiveness versus efficacy
A pragmatic (effectiveness) trial asks whether a drug works in routine care; an explanatory (efficacy) trial asks whether it can work under ideal conditions.
Remember
Efficacy asks whether a drug can work under ideal conditions and effectiveness asks whether it does work in everyday care, so a pragmatic design is the best one to use to decide on routine use of a drug that works under ideal conditions.
An explanatory trial, also called an efficacy trial, tests whether a drug can work under ideal conditions. It uses highly selected patients, and follow-up (the planned checks on participants) is intensive.
A pragmatic trial, also called an effectiveness trial, instead asks whether a drug works in real-world practice. Patients with comorbidities (other long-term illnesses) can take part, because the inclusion criteria (the rules about who may join) are broad. The settings resemble normal NHS care and follow-up is less intensive. That is why the result applies to patients whom a GP will treat.
Efficacy and effectiveness can differ. A drug can show high efficacy but low effectiveness when patients forget doses, cannot tolerate it or differ from the trial population. Real trials sit on a spectrum between the explanatory and pragmatic extremes rather than in one of two boxes.
A pragmatic randomised controlled trial still allocates patients at random. Random allocation on average spreads confounders (other factors that could distort the result) evenly between the groups.
Key facts
- Efficacy
- benefit under ideal conditions, which is what an explanatory trial tests.
- Effectiveness
- benefit in the real world, which is what a pragmatic trial tests.
- Pragmatic design
- less restrictive entry criteria, settings like normal NHS care and less intensive follow-up.
- Explanatory design
- highly selected patients and intensive follow-up, with conditions tightly controlled.
- What each asks
- an explanatory trial asks whether the drug can work; a pragmatic trial asks whether we should use it in routine practice.
- Clue pattern
- routine clinics, comorbidities, variable adherence, meaning how closely patients take treatment as prescribed, and usual follow-up point to a pragmatic trial.
Exam traps
- Testing whether a drug can work under ideal, tightly controlled conditions describes an explanatory (efficacy) trial, not a pragmatic one, which asks whether the drug works in routine care.
- Excluding patients who have comorbidities narrows who can enter and suits an explanatory design, whereas a pragmatic trial uses broader eligibility criteria so that its patients represent those treated in everyday care.
- Close monitoring of adherence, meaning how closely patients take treatment as prescribed, is part of the explanatory approach, where it helps show a drug's effect under ideal conditions, whereas a pragmatic trial uses less intensive follow-up because intensive monitoring can hide the missed doses that happen in everyday practice.
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