Pragmatic and explanatory trials
- Concept
An explanatory trial asks whether something can work under ideal conditions; a pragmatic one, whether it works in everyday practice with real patients.
What it is
An explanatory trial measures efficacy: the effect under ideal conditions, with selected patients, expert centres, monitored adherence and precise intermediate outcomes. A pragmatic trial measures effectiveness: the effect in routine practice, with patients like those in any clinic, ordinary staff and outcomes that matter to patients. These are not two closed boxes but a continuum, and each design sits somewhere on it domain by domain.
Worked example
- Pulmonary rehabilitation programme. Explanatory trial: selected patients, 95 % attendance; admissions at 1 year: 20 % control versus 10 %.
- Explanatory: ARR = 20 − 10 = 10 points; NNT = 1 / 0.10 = 10.
- Pragmatic trial in primary care centres, 60 % attendance: 20 % versus 14 %.
- Pragmatic: ARR = 20 − 14 = 6 points; NNT = 1 / 0.06 = 16.7, rounded up to 17.
- Reading: the programme can work (efficacy), but in real practice 17 people, not 10, must be treated to prevent one admission.
Domains in which they differ (PRECIS-2 style)
| Domain | More explanatory | More pragmatic |
|---|---|---|
| Participants | Strict criteria, no other diseases | Almost everyone who would be treated in practice |
| Setting and staff | Expert centres | Ordinary clinics |
| Intervention | Rigid protocol | Flexible, as it would be delivered in practice |
| Adherence | Monitored and reinforced | Usual |
| Outcome | Intermediate, precisely measured | Important to the patient |
| Analysis | Sometimes per protocol | Intention to treat |
Markers
- Efficacy
- Effectiveness
- PRECIS-2
- ITT
In practice
- Explanatory trials usually come before approval; pragmatic trials inform service and guideline decisions.
- Non-drug interventions depend on the clinician and the setting: there the pragmatic approach matters more.
- Some pragmatic trials use electronic health records to recruit and to measure outcomes.
Common pitfalls
- Calling a trial ‘pragmatic’ when it has strict inclusion criteria and monitored adherence.
- Expecting the same effect in practice as in an explanatory trial.
- Thinking pragmatic means sloppy: randomisation and outcome measurement remain rigorous.
Test yourself
Think of the answer, then tap the question to see it.
What does an explanatory trial measure, and what does a pragmatic one measure?
The explanatory trial measures efficacy under ideal conditions; the pragmatic trial measures effectiveness in routine practice.
Why is the effect usually smaller in a pragmatic trial?
Because it includes more varied patients, lower adherence and ordinary clinicians, which dilute the effect.
Which type of analysis is typical of a pragmatic trial?
Intention-to-treat analysis, which keeps each patient in the assigned group even if they did not follow the intervention.
Connections
Educational content on epidemiological and statistical methods; the examples use made-up numbers to teach the calculation. Not a clinical or legal guide: current Colombian rules are in the official sources.
Sources: CONSORT 2025 Statement: updated guideline for reporting randomised trials (EQUATOR Network, 2025); Chapter 17: Intervention complexity (Cochrane, 2024); Real-World Evidence (U.S. Food and Drug Administration, 2026).
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Representative model, for educational purposes only.