ClinQuiry — Clinical Research, Taught in Sequence

Core summary

Explanatory trials test whether a treatment works under ideal, tightly controlled conditions (efficacy). Pragmatic trials test whether it works in routine clinical practice (effectiveness). Most trials fall on a spectrum between these two extremes.

Detailed explanation

Explanatory trials maximize internal validity through strict inclusion criteria (highly selected patients), standardized protocols, close monitoring, and placebo controls. They answer: 'Can this treatment work?' Pragmatic trials maximize external validity by using broad inclusion criteria (typical patients), flexible treatment protocols, usual care comparators, and clinically relevant endpoints. They answer: 'Does this treatment work in real practice?' The PRECIS-2 (PRagmatic-Explanatory Continuum Indicator Summary) tool scores trials on nine domains from very explanatory to very pragmatic, helping researchers design their trial at the appropriate point on the spectrum. Key domains include eligibility criteria, setting, flexibility of intervention delivery, follow-up intensity, and primary outcome relevance. In reality, most trials are hybrids — the key is to match the design to the research question and the intended audience for the results.

Clinical example

Drug company trial (explanatory): Recruits only patients aged 40-65 with no comorbidities, monitors adherence weekly, uses placebo control, measures a biomarker. Health system trial (pragmatic): Enrolls all adults with the condition, allows usual prescribing flexibility, compares to standard care, measures hospital readmissions.

Research example

The SPRINT trial (intensive vs standard blood pressure control) leaned explanatory — strict protocols, frequent visits. The Salford Lung Study tested an inhaler in routine primary care with minimal exclusion criteria — a highly pragmatic design that enrolled over 4,000 COPD patients in real-world settings.

Knowledge check

Q1. What is the key question an explanatory trial answers?

Q2. Which tool helps researchers position their trial on the pragmatic-explanatory spectrum?

Q3. A pragmatic trial would typically use which type of comparator?