Merging the conceptual framework of implementation outcomes  with an operational framework of social capital [17–20] has the potential to highlight how implementers’ social networks can be leveraged to improve their implementation of EBPs. Below, we explore how bonding social capital, bridging social capital, and their setting-level combination in small world networks can shape individual perceptions, individual use, and setting-level implementation of EBPs (see Fig. 1).
Individual perceptions and bonding social capital
Implementation outcomes of acceptability, appropriateness, and adoption focus on implementers’ perceptions of EBPs and thus can be influenced by implementers’ bonding social capital, which reinforces norms, establishes trust, and cultivates a sense of community [17, 19, 26]. When bonding social capital is high, an implementer is integrated in a dense social network of other individuals, who collectively share norms about how things should be done, and whom the implementer is likely to trust. These shared norms and trust mean that the implementer’s perceptions of an EBP will likely be influenced by, and come to resemble those of, others in their network. As a result, bonding social capital can be a double-edged sword for perceptual implementation outcomes. An implementer with significant bonding social capital where others in their network are enthusiastic about an EBP will also likely find the EBP acceptable and appropriate. In contrast, if others in their network lack enthusiasm for an EBP, the implementer will likely find the EBP unacceptable and inappropriate. Diffusion of innovations theory also suggests that a prospective implementer’s adoption of an EBP depends on its adoption by others, and especially by trusted others such as those in one’s own social network . When a prospective implementer has bonding social capital and others in their network have decided to adopt an EBP, the prospective implementer is more likely to also adopt it. However, if others in their network have not adopted an EBP, the prospective implementer is likely to also not adopt it.
Although outcomes of acceptability and appropriateness are often most relevant in the early stages of implementation, they remain relevant in later stages as implementers update and reevaluate their perceptions. For example, implementers may find hard-to-use EBPs less acceptable after attempting to implement them for a while or may find that an EBP is less appropriate than initially expected after putting it into practice in a specific setting. However, bonding social capital can also be relevant for later-stage outcomes of acceptability and appropriateness. Membership in a dense social network—the hallmark of bonding social capital—provides an implementer with a source of support while confronting the inevitable challenges of EBP implementation. Even if others in the implementer’s network are also experiencing challenges, the mere fact that the network establishes a community struggling with implementation together can mitigate declines in acceptability and appropriateness over time.
Individual use and bridging social capital
Implementation outcomes of feasibility and fidelity focus on implementers’ use of EBPs and thus can be influenced by implementers’ bridging social capital, which facilitates their rapid access to helpful information about how to implement EBPs [17, 19, 26]. Having bridging social capital means that an implementer’s network contacts connect them directly or indirectly with a broad range of sources of information, including those in other parts of their setting (e.g., other teams, departments, or roles) and those outside the setting. Implementers with bridging social capital therefore have access a range of potentially novel (i.e., as opposed to redundant) ideas about how to address implementation challenges when they arise. For example, an implementer who only interacts with colleagues on the same tight-knit team and thus has limited bridging social capital might struggle to find ways to adapt a new EBP to client needs because these colleagues are struggling with the same issues, thus limiting the EBP’s feasibility. In contrast, an implementer who occasionally interacts with others in different roles or departments within their setting, or with an implementer in another state, and thus has high bridging social capital has an opportunity to find ways to make a challenging EBP more feasible by “thinking outside the box” and importing new ideas. Bridging social capital may be particularly important when it links implementers directly or indirectly to an EBP’s development team or other experts in its implementation. Such bridging links mean that implementers can get quicker and more accurate answers to questions about how an EBP should be delivered, thereby boosting the fidelity with which they implement the EBP. Although bridging links do not necessarily connect an implementer with an individual or organization that has relevant information , they do connect an implementer with a diverse range of information, which is nonetheless associated with improved problem-solving [32, 33].
Settings and small worlds
Unlike other implementation outcomes that are focused on individual implementers’ perceptions and use of EBPs, outcomes of cost, penetration, and sustainability focus on the entire setting where implementation occurs. Thus rather than focusing on individual-level forms of social capital (i.e., bonding and bridging), it is more helpful to focus on the structural phenomenon of small worlds, which represents the optimal combination of bonding and bridging social capital at the setting level [19, 28]. A setting will be structured as a small world when participants in that setting (including both implementers and non-implementers) have bonding social capital (e.g., within department-, team-, or role-based clusters), but where a few participants have within-setting ties that bridge across these clusters. However, unlike the implementation outcomes associated with bonding or bridging social capital, we expect that each setting outcome is associated with small world networks for slightly different reasons.
First, although implementation cost can include exogenous factors such as the actual time and financial costs of using an EBP, it can also be impacted by the complexity of the implementation setting itself . Implementation cost will be high in settings characterized primarily by bonding social capital, where participants are in sets of densely connected but isolated groups (see Fig. 2b), because implementation will involve significant redundancies (e.g., multiple trainings must be conducted in each isolated team). Cost will also be high in settings characterized primarily by bridging, where participants lack a clear team structure or hierarchy (see Fig. 2d), because implementation efforts will be difficult to coordinate. In contrast, a setting structured as a small world (see Fig. 2e) balances these competing pressures because the bonding social capital it provides allows coordination within teams, while the bridging social capital it provides allow economies of scale in the delivery of training.
Second, penetration of an EBP’s implementation requires the penetration of two distinct phenomena: implementers’ knowledge about the EBP and implementers’ use of the EBP [9, 34, 35]. A setting structured as a small world is ideal for achieving both. Penetration of implementers’ knowledge about an EBP (i.e., dissemination) is facilitated by the bridging social capital of a small world network, which makes it possible for information to reach all setting participants efficiently. The bridging ties ensure that information about an EBP (e.g., its existence, its basic practices and tools) can spread throughout the entire setting via a relatively small number of intermediaries, which helps transmit the information both quickly and without distortion. Conversely, penetration of implementers’ use of an EBP (i.e., implementation) is facilitated by the bonding social capital of a small world network. The bonding ties form clusters in the setting’s network, which can serve as communities of practice that encourage continued use by providing reinforcement and support to implementers during the implementation process.
Finally, a key challenge to the sustainability of EBP implementation is turnover, which can be high in many social service settings . Frequently, settings are structured hierarchically, where the departure of a single person fragments the network of communication, hampering both trust and information sharing, as well as leading to ambiguity, confusion, and hampered implementation outcomes. In contrast, a setting structured as a small world mitigates the impact of turnover because the departure of one person from the network has little impact on the network’s overall structure . For example, the departure of any one or two individuals from Fig. 2e does not substantially reduce the network’s clustering and setting’s ability to facilitate trust, or the network’s compactness and setting’s ability to facilitate information sharing. Such a setting is resilient to the challenges that accompany turnover and thus is more likely to facilitate the sustained implementation of an EBP when turnover is inevitable.