Implementability of healthcare interventions: an overview of reviews and development of a conceptual framework

Implementation science aims to identify and address care gaps, support practice change and enhance quality and equity of health care. Building a robust and generalizable evidence base to inform implementation practice is the objective of implementation research. Implementation research can also play a critical role in efforts to reduce research waste, in that it can provide evidence about the strategies that are effective for translating the findings of clinical research into enhanced healthcare practice and thus improved health outcomes [1‐3]. Identifying the factors important for translation of an effective intervention or innovation from the research setting to routine clinical practice can arguably contribute to reducing the estimated annual US$85 billion, globally, wasted in health research [1, 2, 4].

Most implementation investigations focus on one of two approaches to achieve change. First, implementation activities consist of either “top down” processes (e.g. governance arrangements, national policies and guidelines, continuing medical education, incentivisation systems) [5‐7], or more granular “bottom-up” processes that consider views of healthcare workers: their perceived barriers and enablers to specific elements of practice change at the level of healthcare teams and individual clinicians [8‐11]. The second approach considers features of healthcare contexts (including organisational factors and the wider health system context) that might interact with the implementation activities to enable or impede practice change [12‐16].

The current paper considers a third lever for achieving implementation: the perceived features of healthcare interventions themselves (in addition to effectiveness). An early theory, Diffusion of Innovations [17], identified six features of innovations that make their adoption more or less likely, namely, relative advantage, compatibility with the existing system, complexity, trialability, potential for reinvention and observed effects, where trialability refers to being able to test the innovation or intervention on a small scale, such as a pilot study. The more recent Consolidated Framework of Implementation Research (CFIR) proposed seven attributes of interventions, namely, intervention source, evidence strength and quality, relative advantage, adaptability, trialability, complexity and design quality and packaging, which refers to the presentation of the intervention, such as how it is bundled and user accessibility [12]. A recently published review identified 28 implementation frameworks and models, including the CFIR, which were synthesised into a number of core phases and components [18]. The authors suggest there is a need for an overarching framework that can guide researchers from intervention development to sustainable practice change.

Uptake of an intervention by both providers and recipients also depends crucially on their perceptions of the intervention. The COVID pandemic of 2020–2021 exemplifies this point. Even though approved vaccine interventions have substantial evidence of a positive benefit-to-risk ratio, the speed of uptake in many countries has been dependent on the perceptions of politicians, service providers and members of the public regarding the necessity, urgency and benefits of vaccine programs. It seems that, independent of the objective features of an intervention, stakeholder perceptions about the intervention will radically influence implementation and uptake at many levels. Furthermore, these perceptions may change over time and during roll-out of an intervention. We refer to these perceptions as views about the “implementability” of an intervention. We define “implementability” as the likelihood that an intervention will be adopted into routine practice and into health consumer behaviours across settings and over time. Several concepts related to implementability of healthcare interventions are gaining traction in the implementation science literature and appear to be primarily focused on the earlier stages of intervention development or latter stages of evaluation. These are acceptability, fidelity, feasibility, scalability and sustainability. A search of the health sciences literature (conducted 25th February 2021) for studies published in the last 20 years containing one or more of these five concepts in the title, revealed that the annual frequency of usage has steadily increased. Figure 1 shows that, from a relatively low baseline in the year 2000, these concepts appeared in titles in 2020, respectively, > 900, > 450, > 4500, > 350 and > 650 times.

Where there was an explicit rationale in the included studies, authors noted that the concept under investigation was likely to influence engagement, adoption and ongoing use. For example, a systematic review exploring videoconferencing in an orthopaedic setting [19] found that “acceptability of service users (both patients and clinicians) is a key factor for the uptake of telemedicine in clinical practice” (p.184). Hence, it is plausible that these concepts, individually and collectively, influence intervention implementability. To identify whether other implementation-related concepts were also appearing in the literature, we conducted a further illustrative search of literature published in the last 20 years (conducted on 29th August 2021) relating to specific interventions (using the phrase “of [intervention]”). We selected three healthcare interventions for which there were published reviews including one or more of the five concepts. The majority (> 90%) of reviews focused on clinical effectiveness or evaluation of outcomes. No additional concepts related to implementability, other than the five considered in our proposed framework, were evident.

There seems to be little consensus about the nature of these concepts, appropriate measurement strategies and how they might be related to one another. Without consistent definitions or reliable measurement approaches, it is not possible to test assumptions or predictions about whether these features indeed influence the implementability of healthcare interventions.

Implementability has been previously explored in the published literature, but this has focused on the implementability of clinical practice guidelines [20‐23] or, more recently, the implementability of late-phase clinical trials [24]. The current paper focuses more broadly on prospective implementability of healthcare interventions, particularly at the early stages of development and evaluation, during scale-up, and over time.

The aim of this paper is to report the development of a testable conceptual framework of implementability that includes acceptability, fidelity, feasibility, scalability and sustainability.

A multifaceted approach was used to develop and refine the framework of implementability of healthcare interventions. We use the World Health Organization definition of healthcare interventions as “an act performed for, with or on behalf of a person or population whose purpose is to assess, improve, maintain, promote or modify health, functioning or health conditions.” [25]

Based on the findings from the overview of reviews and the group consensus process, we propose a framework of implementability of healthcare interventions which includes five key concepts, namely, acceptability, fidelity, feasibility, scalability and sustainability. The framework illustrates the interrelationship between the concepts and chronology, with acceptability, fidelity and feasibility requiring investigation during early stages of the development of a healthcare implementation, including during proof-of-principle studies and pragmatic evaluations of intervention effectiveness at one point in time and in one specific context. Acceptability is a necessary but not sufficient condition for fidelity, and similarly, fidelity is a necessary but not sufficient condition for feasibility. All three concepts are context- and population-dependent and will require reinvestigation as the healthcare intervention is scaled to different settings and populations and over time. We argue that there is an association between the concepts, with acceptability, fidelity and feasibility influencing the scalability and sustainability of a healthcare intervention. We are not suggesting that there is a causal relationship between the concepts, rather, scalability and sustainability depend on the pre-conditions acceptability, fidelity and feasibility of the healthcare intervention, and these concepts should be re-examined over time, and as the healthcare intervention is implemented with different populations or in different settings. This argument is consistent with other frameworks on scalability and sustainability, including the Intervention Scalability Assessment Tool [82] and the Dynamic Sustainability Framework [98], both of which suggest that feasibility, acceptability and fidelity must be considered in the planning for scaling up and sustainability of a healthcare intervention. The Consolidated Framework for Implementation Research [12] suggests that the outer setting, including the social and economic context, can influence implementation. Our proposed framework encourages the researcher to prospectively assess acceptability, fidelity and feasibility in both the inner and outer contexts as the key stakeholders are likely to be different.

From the 252 reviews identified in the overview, the majority did not provide a definition of the concept. Rather, the reviews used measurement approaches which implied a definition. For example, feasibility was typically defined by measuring components such as compliance to the intervention, dropouts, recruitment rates and adverse events. There was conflating of terms, with feasibility and safety used interchangeably in several reviews, particularly drug feasibility reviews. Although frameworks were identified for all five concepts, they were not frequently used in the reviews identified in the overview. Most of the frameworks included conceptual definitions and operationalisation of the concept, but these varied between frameworks. It is difficult to test the influence of these concepts on the implementability of a healthcare intervention without consistent definitions, descriptions, operationalisation and measurement approaches for these concepts.

Of all the concepts explored in the systematic overview, scalability and sustainability of healthcare interventions were not often achieved. These findings suggest that healthcare interventions may be found to be effective, acceptable and feasible in the development or pilot phase, but this does not guarantee successful scale-up or sustainment of the intervention over time. We propose that the framework of implementability can provide a dynamic, longitudinal perspective of intervention development where researchers consider acceptability, fidelity and feasibility during the earlier phases of intervention development and implementation, and iteratively re-evaluate these factors as the healthcare intervention is scaled to different settings and over time.

Other rigorous frameworks, such as RE-AIM and the Implementation Outcomes Framework, propose that sustainable adoption and implementation of healthcare interventions require consideration of many like concepts such as acceptability, reach, effectiveness, adoption, implementation and maintenance [99, 100]. Whilst there are some similarities in the concepts contained in these frameworks and our proposed framework of implementability, the latter is explicitly concerned with the prospective and ongoing identification of factors that will influence scalability and sustainability of a healthcare intervention. It should also be noted that prospective identification of factors that influence implementability of healthcare interventions is receiving growing attention in the literature, particularly in relation to reducing avoidable research waste [101]. A recent publication developed a framework to assist researchers to prospectively cost the different phases of healthcare interventions. The authors argue that implementation costs are often underestimated or not included in cost-effectiveness analyses. This in turn contributes to research waste which may have been avoided through a more systematic and earlier approach to identifying the factors that support the translation of effective interventions into real-world settings, and prospectively costing the implementation of these.

It has been argued that involving end-users in the development and implementation of healthcare interventions may improve outcomes through enhanced relevance, acceptability and feasibility [102]. We propose that our framework of implementability could be used to test these assumptions. We recommend that researchers prospectively set criteria to inform the decision about whether to abandon, amend or proceed with the intervention, depending on the outcomes of the feasibility study [103]. Table 12 illustrates how the framework of implementability could be used to prospectively guide the ongoing implementation activities of healthcare interventions. Enabling factors were identified from published frameworks and reviews included in step 1, though this is not an exhaustive list and is likely to be influenced by context. For example, scalability of healthcare interventions to low- and middle-income countries may be more, or less, enabled by factors that differ from those in high-income countries [104]. The framework of implementability of healthcare interventions may be particularly helpful in guiding effectiveness-implementation hybrid designs, which aim to simultaneously evaluate effectiveness of the intervention in the real-world context and the implementation strategy [105‐107].

We propose that empirical investigation of the framework of implementability is required to answer the following questions:

What is the nature of the relationship between the key concepts? (e.g. linear, curvilinear or threshold?)

Do acceptability, fidelity and feasibility predict scalability and sustainability as proposed in the framework?

Can identified deficits in constructs of the framework be addressed to enhance the implementability of effective interventions?

To our knowledge, this is the first review that considers all five key concepts in published reviews on healthcare interventions. The overview collated and described important information on concepts that are increasingly being assumed to influence implementation of healthcare interventions. The development of a framework utilising well-established consensus methods is another strength. Although one author was responsible for most of the screening, data extraction and coding, independent extraction by a second author of 10% of the reviews confirmed reliability of the extraction process.

In order to the make the overview of reviews feasible, we only focused on publications that had one or more of the concepts in the title and/or abstract. Therefore, it is possible we may not have identified some reviews that were relevant. It must also be noted that the framework of implementability of healthcare interventions is untested. We propose that it articulates some of the untested assumptions in the current literature on implementation science and have suggested some approaches for empirical evaluation of the framework.

We do not propose that interventions with high implementability will automatically result in high uptake. As we argued in the background to this paper, the features of interventions may interact with top-down and bottom-up implementation activities, and with contextual factors, to achieve consistent uptake into routine practice. Our argument is that these implementation activities are more likely to be effective if implementability of the intervention is high.

The framework developed in this study can inform research that aims to prospectively and iteratively identify the likely implementability of evidence-based healthcare interventions. We suggest that the framework be tested empirically through studies that examine the actual uptake of interventions, across settings and over time, compared with prospective assessments of the independent variables (acceptability, fidelity and feasibility) and the outcome variables (scalability and sustainability) in the framework. We recommend that, to avoid research waste, implementability should be assessed, and enhancements made, during the clinical evaluation stages of the development of interventions [1, 3]. This would potentially accelerate their uptake into clinical practice.