Implementation and hybrid studies
Why this level?
The design family and its defining features have not been specified for this hierarchy. NHMRC 2009 sourceA hybrid design pairs an effectiveness question with an implementation one. The level follows the effectiveness half; the implementation half asks how something is delivered, which is not what this hierarchy rates.
What question does this help answer?
Not does this work, but does this get done. Most effective interventions in medicine are under-used, and the reasons are organisational rather than biological, so they need their own evaluation.
Intervention and strategy are two things
The intervention is what reaches the patient: the drug, the checklist, the physiotherapy. The implementation strategy is what reaches the clinician or the system: the training, the audit and feedback, the reminder, the champion, the change to the electronic record. An implementation study manipulates the second, and both must be described separately, in enough detail to be reproduced.
Hybrid designs
A hybrid study takes both on at once. Type 1 tests the intervention's effectiveness while gathering information about implementation. Type 2 tests both. Type 3 tests the implementation strategy while watching the clinical outcome. Naming the type is what tells a reader which claim the study is powered for; a hybrid that reports the clinical outcome as its headline while having been designed as a type 3 has overreached.
Where the hybrid types sit
Outcomes are their own set
- Implementation outcomes: adoption, reach, acceptability, feasibility, fidelity, penetration, sustainability, cost.
- Service outcomes: timeliness, safety, equity, efficiency.
- Clinical outcomes: what happened to patients.
- Fidelity in particular is not optional. Without it, a null result cannot distinguish a strategy that does not work from one that was never delivered.
- Equity of reach deserves separate reporting: a strategy that improves the average while widening a gap has not succeeded.
Common designs
Cluster randomization, stepped-wedge rollout and interrupted time series are all common here, because the unit that adopts a strategy is usually a ward, clinic or hospital rather than a patient. Each carries its own clustering requirements, and those apply exactly as they would anywhere else.
Why Mallard may recommend it
Mallard may point here when a description is about uptake, adherence to a guideline, de-implementation of something ineffective, or spreading a practice that already has evidence behind it.
How it is sized
Sizing follows the design that carries it. A cluster-randomized or stepped-wedge implementation study is sized as one, with the intracluster correlation and the number of clusters governing, and Mallard sizes those by simulation rather than a closed form. The implementation outcome and the clinical outcome will not require the same sample size, and the study must say which one it is powered for.
What to watch out for
Effectiveness and implementation are different outcomes and a study that measures only adoption cannot say the intervention worked. Fidelity must be measured, because a null implementation result is ambiguous between an ineffective strategy and one that was never actually delivered.
Clinical example
Question: How do we get sepsis bundles used on medical wards? Design: Randomize wards to an audit-and-feedback strategy or usual dissemination, measure bundle completion as the primary implementation outcome with fidelity of the feedback itself recorded, and report mortality as a secondary outcome the study is not powered for.
How to report it
StaRI is the guideline for this design. It is built around reporting the implementation strategy and the intervention as two separate objects, each with its own description, outcomes and results, which is exactly the distinction this design turns on. A reporting guideline is not a design manual: use it to make the study transparent, not as a substitute for careful design. Check the target journal's own requirements as well, which this page cannot know.
- Standards for Reporting Implementation Studies (StaRI) Statement (opens in a new tab) · BMJ · doi 10.1136/bmj.i6795
- Effectiveness-implementation hybrid designs: combining elements of clinical effectiveness and implementation research to enhance public health impact (opens in a new tab) · Med Care · doi 10.1097/MLR.0b013e3182408812