Prior to conducting the review, the body of working theories that 'lies behind the intervention' needs to be identified. Pawson suggests tapping into stakeholders and experts as an initial strategy to help frame the problem [
22,
26]. Our approach to exploring key theories will begin by consulting with clinician scientists and experts in guideline development and knowledge translation to better understand perceptions of guideline implementability before searching the literature to identify 'theories, hunches, expectations, and the rationalizations' for why they may or may not facilitate knowledge uptake [
22,
25]. The goal of this exercise is not to collect data about the efficacy of guidelines but to identify a range of theories and explanations for how guidelines are supposed to work (and for whom), when they do work, when they don't achieve the desired change in practices, why they are not effective in this, and why they are not being used. The body of literature from exploring key theories will be representative of our first stage of literature searching (
i.e., the core articles search as described below), from which we will build a working list of candidate theories (
i.e., middle-range or 'educated guess' theories). These candidate theories will be continuously tested and appended as they evolve (or new theories emerge) and will be finalised only when their validity has been tested and explored during the realist-review process [
22,
27].
Well-studied theories related to changing behaviour include the Social Cognitive Theory [
28], the Theory of Reasoned Action [
29], the Theory of Planned Behaviour (TPB) [
30], the health belief model [
31], stages of readiness to change [
32], and Rogers' Diffusion of Innovations Theory [
33]. To guide our exploration of which perceived factors influence guideline adherence, we will use the TPB, as it is the most widely researched, influential, and empirically based framework designed to predict and explain human behaviour in specific contexts [
30,
34]. According to the TPB, human behaviour is guided by three types of motivational factors that can lead to intention to perform the target behaviour: (1) attitudes toward the behavior, (2) subjective norms (
i.e., a person's perception of injunctive norms [behaviours perceived as being approved by other people] and descriptive norms [people's perception of what is commonly done in specific situations]), and (3) perceived behavioural control [
30]. In the context of guideline implementability, the central behavioural goal is to 'use' or 'uptake' guidelines. These intentions can be illustrated according to the three conceptually independent predictor variables. The first can be conceptualised as the attitude or behavioural beliefs toward using guidelines and refers to the degree to which a person has a favourable or unfavourable evaluation of this behavioural goal (
i.e., the strength of their intention or motivation). The second predictor is normative beliefs (
i.e., the subjective norm), which refers to the perceived social pressure to use or not use guidelines. The third predictor is the degree of perceived behavioural control, which can be conceptualised as the perceived ease or difficulty of performing guideline use or uptake. This may reflect past experiences as well as anticipated impediments and obstacles of the behaviour. Together, these three predictor factors can lead to the formation of behavioural intention. In general, we can predict that the more favourable the attitude and subjective norm with respect to using guidelines, and the greater the perceived control, the stronger the individual's intention to adhere to them. Intention is thus an immediate antecedent of guideline use, but the degree of success will also depend on other nonmotivational factors, such as availability of requisite opportunities and resources (
e.g., time, resources, skills, willpower) [
30]. Based on the TPB, it is expected that intentions to use/uptake guidelines will be predicted from attitudes, subjective norms, and perceived control with respect to this goal and that intentions and perceived control may in turn permit prediction of actual adherence to guidelines.