Behaviour change interventions (e.g., to increase physical activity, adherence behaviours, screening attendance) are typically complex, involving many interacting components. We need methods of specifying and reporting complex interventions in order to strengthen the knowledge base required for such interventions to be more effective, replicable, and implementable. The complexity of interventions to change behaviour is determined, in part, by the number of components involved. Components include the techniques to facilitate behaviour change that constitute the active ingredients of the intervention and procedures for delivery of those techniques. Procedures for delivery include who delivers the intervention, to whom, how often, for how long, in what format, and in what context . The UK Medical Research Council's guidance  for developing and evaluating complex interventions acknowledges the need for improved methods of specifying and reporting intervention content. The CONSORT statement for randomised trials of nonpharmacologic interventions calls for precise details of the intervention, including a description of the different intervention components . It is important to specify and report both the active techniques and procedures for delivery. This protocol focuses on the former, that is, methods for specifying what is delivered, rather than on how it is delivered. It addresses techniques that target the behaviour of individuals but that may be delivered in a variety of ways (e.g., prompts or reminders delivered by a 'buddy', telephone call from a healthcare professional, postal leaflet, or environmentally, such as hand-washing signs). By technique, we mean a replicable component of an intervention designed to alter or redirect causal processes that regulate behaviour; that is, a technique is proposed to be an 'active ingredient' (e.g., feedback, self-monitoring, and reinforcement). Techniques also have specified criteria for their operationalisation, that is, minimum delivery specifications that would allow identification of that technique (e.g., feedback must involve providing the target audience with information about their behaviour). The identification of behaviour change techniques (BCTs) is critical to understanding how organisational change and national policy changes (including policies around access and price) have their effects on individuals' health-related behaviours.
Despite the considerable investment in randomised controlled trials (RCTs) of complex interventions and in systematically reviewing their effects, interventions tend to be poorly described and reported. There is no consensus on terminology, and descriptions of interventions lack the specificity required for replication [2, 4–6]. When secondary data analyses are conducted to ascertain which types of interventions are effective, many are too poorly specified to be included ; there is no consensus on how to classify content, and, therefore, each analysis develops its own classification system [1, 8]. This results in much wasted effort since there is no common method for synthesising the findings of primary studies in a conceptually coherent way. Further, unless we can specify the active BCTs delivered within the standard care or control group, replication and accurate implementation is difficult or even impossible, and effect sizes for new interventions will continue to be uninterpretable . These problems are evident across a wide variety of large, expensive trials of public health [10–12] and implementation interventions . This impedes the accumulation of knowledge and implementation of effective behaviour change interventions . In a 2008 address, the President of the Association for Psychological Science stated, 'For psychological research to flourish and develop into an increasingly cumulative basic science, there are some fundamental requirements. It's essential to develop and use common shared tools and a common language, so that replication, and building on solid work, becomes accepted practice and is valued (http://www.psychologicalscience.org/observer/getArticle.cfm?id=2430).'
Scientific advance requires an agreed-upon and reliable method of specifying and labeling BCTs . Behavioural science has provided us with myriad potential BCTs [5, 15, 16], but there is no agreement on how they are labeled and identified. The same technique may be described by different labels (e.g., 'self-monitoring' may be labeled 'daily diaries'), and the same labels may be applied to different BCTs (e.g., 'behavioural counseling' may involve 'educating patients' or 'feedback, self-monitoring, and reinforcement' ). Imprecise labeling may lead to misleading conclusions in evidence synthesis. As a result of under-specification, behavioural medicine researchers and practitioners have been found to report low confidence in their ability to replicate highly effective interventions for diabetes prevention . This problem needs to be solved to strengthen behavioural science and improve behaviour change intervention effectiveness.
Despite recommendations for describing intervention components [2, 3], no rigorous and widely accepted methodology for doing this has been suggested. We propose to develop a systematic, referenced nomenclature (a system of technical terms used in a science, such as the periodic table of elements in chemistry or the biological classification) of BCTs with fully operationalised definitions to enable replication. This will form the basis of a future hierarchical classification (or 'taxonomy'). Describing behaviour change intervention content by a systematically produced, reliable nomenclature will strengthen the following:
1. Knowledge base: Published reports of intervention studies will be able to provide more detail on the BCTs, making effective interventions easier to replicate in primary research. They will also be able to specify 'standard care', thus ensuring that evaluated interventions are actually different from standard care comparator conditions. Systematic reviewers will be able to use a reliable method for extracting information about intervention content, thus identifying and synthesising discrete, replicable, potentially active ingredients associated with effectiveness. A shared language has allowed us and other reviewers to use an early version of a technique nomenclature to synthesise heterogeneous interventions and use meta-regression to determine which component BCTs are effective [8, 9, 15, 18, 19]. For example, a systematic review of 122 evaluations of interventions to increase physical activity and healthy eating  found that the technique 'self-monitoring' explained the greatest amount of among-study heterogeneity (13%). Interventions that combined self-monitoring with at least one other theoretically derived technique were significantly more effective than the other interventions (pooled effect sizes of 0.42 vs. 0.26, respectively). Another example of a study using this method reanalysed a Cochrane review of audit and feedback interventions and allowed the investigation of the separate effects of goal setting, monitoring, and action plans .
2. Evaluation and implementation: In RCTs evaluating behaviour change interventions, effect sizes will be interpretable in the context of clear specification of both intervention and control groups. Intervention developers will be able to use a comprehensive list of BCTs (rather than relying on the limited set they are aware of) to produce guidelines about how to operationalise the BCTs in protocols for implementation.
Development of a preliminary list of BCTs
As a first stage, we have reliably identified a set of 26 BCTs from 195 published descriptions of behaviour change interventions to increase physical activity and healthy eating , demonstrating the feasibility of a method for developing standardised labels and definitions of BCTs included in complex interventions and specifying behaviour change interventions in terms of a defined list of BCTs. We subsequently extended this list to a wider range of behaviours, drawing on systematic reviews  and an analysis of relevant textbooks, reliably identifying 54 BCTs . Further work is needed to extend the list to a wider range of types of behaviour and to improve the definitions of approximately 50 additional BCTs that were poorly specified (some similar BCTs were referred to by a variety of labels, and some labels were unclear or overlapping). More recently, we, and others, have extended the list to techniques designed to change other behaviours (e.g., smoking) and populations (e.g., obese patients) [18, 19]. At this stage, we are limiting the project to behaviour change interventions targeting individual behaviours because of the time and resources required, while recognising the need to extend this to other types of complex interventions that target different levels of healthcare systems .
Few systematic reviews of behaviour change interventions use nomenclature systems [21, 23, 24]. Our preliminary BCT list, developed and evaluated using systematic methods to assess interrater reliability, has been widely used internationally, within a short period of its publication (2008), to report interventions , synthesise evidence [9, 18, 19], and design interventions . Subsequently, we were invited to write journal editorials that have influenced editorial policy, requiring specification of complex intervention components to be based on reliable methods (e.g., in Addiction and Implementation Science), and a group of 12 international journal editors have built on this to widen the call for developing reporting methods, forming the Workgroup for Intervention Development and Evaluation Research (WIDER, http://interventiondesign.co.uk/?page_id=9). This evidence of uptake supports the need for, and usability of, a nomenclature system.
Given the impact of our initial work, it is important to extend, consolidate, and enhance the generalisability of this method by building a wider, international consensus and disseminating and evaluating the nomenclature.
Our goals for this project are as follows:
To develop a reliable and generalisable nomenclature of BCTs as a method for specifying, evaluating, and implementing complex behaviour change interventions
To lay a foundation for
a comprehensive methodology that can be applied to many different types of complex interventions, including organisational and community interventions
a fully developed, hierarchically organised taxonomy of BCTs
To achieve multidisciplinary and international acceptance and use to allow for its continuous development
Our objectives for this project are as follows:
Development: Generate an extensive list of clearly labeled, defined, nonredundant BCTs as the basis of the nomenclature (phase 1).
Evaluation: Test the reliability and usability of the preliminary nomenclature across different behaviours and populations (phase 2).
Prototype nomenclature: Produce a nomenclature with definitions and guidance on its use, evidence of consensus, evidence of reliability, and usability of each BCT, illustrated with examples from effective interventions (phase 3).
Implementation and dissemination: Make the nomenclature and its method of development widely accessible through a systematic dissemination plan (cross-phase).