Design
Purpose
Explanatory
Designed to answer a simple question: does the intervention work? If yes, how does it work?
Pragmatic
Designed to determine if the intervention works and also describes all the consequences of the intervention and its use under circumstances corresponding to daily practice
In practice, most randomized controlled trials combine elements of both—explanatory and pragmatic trials.
The various descriptions of trials are related to the expected outcomes, participant’s exposure, and masking. They are shown in Table 31.2.
Table 31.2
Phases and designs of clinical trials
Phase | When | What | |
|---|---|---|---|
Phase | 1 | Safety study in human volunteers | After the animal safety is proven, phase 1 is performed in healthy volunteers; this phase of clinical trial documents the safety of the intervention in humans |
2 | Efficacy and safety in human subjects | Evaluates the efficacy of the intervention while still providing information on safety | |
3 | Effectiveness study | Randomized trials to assess the effectiveness of the intervention | |
4 | Post-marketing study | Identifies and monitors possible adverse events not yet documented | |
Design | Parallel | Each group of participants is exposed to only one of the study interventions | |
Crossover | Each of the participants, randomly assigned order, is given all of the study interventions in successive periods | ||
Factorial | Two or more experimental interventions are evaluated separately and also in combination and against a control | ||
Masking | Open | Everybody involved in the trial knows which intervention is given to each participant
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