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Michie S, Wood CE, Johnston M, et al. Behaviour change techniques: the development and evaluation of a taxonomic method for reporting and describing behaviour change interventions (a suite of five studies involving consensus methods, randomised controlled trials and analysis of qualitative data). Southampton (UK): NIHR Journals Library; 2015 Nov. (Health Technology Assessment, No. 19.99.)

Cover of Behaviour change techniques: the development and evaluation of a taxonomic method for reporting and describing behaviour change interventions (a suite of five studies involving consensus methods, randomised controlled trials and analysis of qualitative data)

Behaviour change techniques: the development and evaluation of a taxonomic method for reporting and describing behaviour change interventions (a suite of five studies involving consensus methods, randomised controlled trials and analysis of qualitative data).

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Chapter 8General discussion and conclusions

We have outlined the need for a reliable method for specifying the content, or ‘active ingredients’, of BCIs, a difficult task given that they are complex and often involve several interacting techniques. However, such a method is necessary to enable more effective evaluations of intervention effectiveness, improved evidence synthesis and more accurate replication of intervention content in science and delivery.

When this project began, there was widespread and growing use of the taxonomy developed by Abraham and Michie20 and various research groups were developing their own taxonomies for application to different kinds of intervention. Therefore, it was important to co-ordinate this activity to ensure that a proliferation of taxonomies did not create the same ‘Tower of Babel’ as that produced by previous unco-ordinated methods of reporting. In order to achieve this, our starting point was all the published BCT taxonomies (e.g. smoking,27 physical activity and healthy eating,28 excessive alcohol use29 and condom use30), which we then developed into BCTTv1 using a systematic process and involving authors from each of these taxonomies. In order to ensure international input and to build international consensus for the work, a further early step was to invite world experts across a range of countries, disciplines and research areas to join an IAB. A wide range of experts from multiple disciplines and countries were involved throughout the project.

The major output of this work, BCTTv1, is a resource for intervention designers, researchers, practitioners, systematic reviewers and all those wishing to communicate effectively about the content of BCIs. This taxonomy was developed and evaluated in a series of stages involving 400 behaviour change experts. The stages consisted of:

  • initial prototype development
  • a two-round modified Delphi procedure
  • Feedback from the IAB
  • feedback from study team members
  • investigating hierarchical structure within the taxonomy using both an open-sort and a theory-driven methodology
  • developing and evaluating training in the use of BCTTv1 for coding intervention descriptions
  • testing the reliability and validity of using the taxonomy to specify intervention content
  • testing the utility of the taxonomy in reporting intervention descriptions.

This resulted in a hierarchical taxonomy of 93 distinctive, non-overlapping BCTs clustered into 16 groupings, each with a clear label, definition and examples. The value of this resource is demonstrated by the number of people wishing training in its use. To date, we have trained 350 people in eight full- and four half-day workshops and 75 people in group tutorials. Owing to increasing demand, we have launched a free, open-access online training resource and smart phone application to allow easy retrieval of BCTs (see www.ucl.ac.uk/health-psychology/bcttaxonomy/97).

The process of development was intensive, effortful and time-consuming, reflecting its complex nature and the need to achieve broad, international consensus. In effect we were producing a new dictionary and so had to reconcile nuances and ambiguities in the meanings of words to ensure that the BCT labels were understood by all users in the same way. The process involved much iteration through testing, refinement and consultation with 77 users and training 351 coders and writers in the taxonomy to identify BCTs in descriptions and report observed interventions. The amount of work involved should not be underestimated but it has produced BCTTv1, a comprehensive cross-behaviour and consensus-based BCT taxonomy representing significant progress towards a shared language for reliable and accurate description of intervention content.

The large number of distinct BCTs generated, combined with the detail needed to achieve precision in the definitions, raised the need for structure within the taxonomy. The reliability testing revealed that reliable use of BCTTv1 would be enhanced by training in addition to simply publishing BCTTv1 as a list of BCTs for people to use. The following sections discuss the work we did to develop the structure of the taxonomy and a comprehensive training programme, and assess its reliability, validity and usefulness for writing observed interventions.

Creating a structure for Behaviour Change Technique Taxonomy version 1

The recognised need by the BCCTv1 study team and the IAB to produce a structure for BCTTv1 to make it more usable and BCTs easier to find raised several issues. The first was whether to create a theory-driven, top-down structure or whether to create a more pragmatic, bottom-up structure that reflected a shared way of thinking about BCTs among users with different theoretical perspectives and/or disciplinary backgrounds. The general view of the IAB and the study team was that it would be more important to start by adopting a pragmatic, bottom-up structure as it would enable use of the structured taxonomy by users with very different backgrounds and would form a basis for consensus on its use and future development.

The second issue concerned the nature of the groupings produced. Despite not explicitly drawing on theory, the BCT groupings appeared to make theoretical sense. Therefore, we explored the relationship between the obtained structure and an alternative structure generated by people using a simple integrated classification of theoretical constructs. We found moderate overlap between the two structures, suggesting that apparently a theoretical use of BCTs may involve implicit theory.

To increase the applications and impact of BCTTv1, work has begun to establish linkage between BCTs and behaviour change theory in order to increase the BCTTv1’s usefulness for designing theory-based interventions,45 as well as understanding effective interventions in terms of theoretical mechanisms21,24,49,159 testing theory. A large number of theories have been used to explain behaviour change, with a recent review identifying 83.160,161 Just as developing a consensus list of BCT labels and definitions required intensive work to develop a methodology, so developing a consensus about how BCTs link to theoretical mechanisms will require intensive work to develop a methodology. This work has begun, funded by the UK’s MRC.138

Coding of behaviour change techniques as a trainable competence

Our experience has shown that a large number of users and potential users wish to undergo formal training in the use of BCTTv1. We showed that both workshop and distance group tutorial training formats increased validity of coding BCTs in intervention descriptions. Although there is room for improvement, we showed that training by either method increased the percentage of trainees achieving an acceptable standard of coding competence as indicated by agreement with expert consensus (75% for tutorials and 45% for workshops). In study 4 (see Chapter 5), a subgroup of trained coders then went on to successfully apply their knowledge and skills to a more extensive coding exercise, achieving good reliability at baseline and at 1 month later. The likely future identification of further BCTs in addition to the already extensive nature of BCTTv1 mean that maintaining reliability and accuracy in using the taxonomy becomes more challenging. Data from the training evaluation and trainee feedback have informed the development of an open-access, online assessment and training course based on our tutorial training model96 (see Chapter 4, Methods; see www.ucl.ac.uk/health-psychology/bcttaxonomy/97). As face-to-face training, delivered either in a 1-day workshop or distance group tutorial format, is labour intensive for the trainers, the study team has been unable to meet the demand from users wanting to be trained. The online training course will allow new users to develop BCT coding competence and will allow experienced users to upgrade their skills and assess their level and pattern of competence. This remains to be evaluated and we are not yet in a position to offer training or assessment of skills in using BCTTv1 to report intervention descriptions.

Reporting interventions

We expected that training in BCTTv1 would lead to better, that is clearer, more readily replicable and more recognisable intervention descriptions. This is not what we found. Our training was as likely to make the descriptions worse as it was to improve them, although it was limited to the context of reporting interventions for which the only source of information was watching a brief video. Therefore, although the findings of our studies did not support the added value of using BCTTv1 in reporting observed interventions, the nature of the task was rather artificial and so probably not a good test. Therefore, we can make no recommendations for using the BCTTv1 at this stage and further research to investigate this is urgently needed.

However, we continue to think that this is an important objective and, as indicated in Chapter 6, there are certain avenues that we would wish to explore to achieve a better understanding of the results we obtained. There are issues to do with the design, the assessment measures and the training package we used, but perhaps a key issue is the nature of the reporting task we used. While the task involved reporting an intervention, it is not a task that would normally be undertaken in either a practice or a research setting. We would not normally produce a description of an intervention after observing it, unless it is an existing intervention in clinical practice or policy settings and no manual or protocols are available. We would be much more likely to write an intervention description before its delivery (i.e. for inclusion in the study protocol) and once intervention delivery has been completed (i.e. when reporting for evaluation and publication). In retrospect, a better test of BCTTv1 for this purpose would be to investigate whether use of BCTTv1 enhances existing intervention descriptions rather than using it to create descriptions simply from observation, or whether it enhances intervention reporting after trainees have had the opportunity to integrate the taxonomy into their normal reporting style. For example, authors of published intervention protocols or existing manuals routinely used in clinical practice or policy settings might be invited to rewrite the intervention description using BCTTv1 and research participants asked to choose the ‘better’ description from each pair of old and new descriptions.

Strengths and limitations

The work conducted in this series of studies represents a step-change in the methodology for reporting the content of BCIs. However, it also has limitations in both the methods used and the product. Constraints in terms of both time and financial resources meant that recruitment was conducted via known networks and contacts, with the result that the 400 people involved in the work were predominantly from Europe and the USA, with only a sprinkling from countries beyond this. There was also an unevenness of disciplines involved in the work, the majority being psychologists. Whilst psychologists are likely to be familiar with behaviour change concepts and therefore likely to be relatively easy to train to use the taxonomy, its wide application will require usability across a range of backgrounds and expertise. We engaged one lay participant in the study to check comprehensibility of materials. Future work should extend this to a wider range of lay perspectives and to engagement with dissemination as well as development activities.

The aim of the work was to develop and evaluate the usefulness of the BCT approach to specifying interventions, that is demonstrate ‘proof of principle’ rather than to produce a finished product and training programme. In fact, when we designed the studies we had not envisaged developing a training programme; the need for this emerged as the size of the taxonomy emerged. Given resource constraints, we decided to train participants in 24 of the most common of the 93 BCTs, as this would be likely to be most useful and familiar to them and, therefore, likely to be learned most quickly. It may be that the less-familiar BCTs are more difficult to teach to the competence criteria and would need more intensive and longer training than was provided in this project.

The training was four distance group tutorials, which is substantially less than the training that the authors’ research groups used when applying precursor taxonomies. Although this is sufficient to train the principles underlying the use of the taxonomy and to get an acceptable degree of inter-rater reliability and agreement with expert judgements, our findings show that more training is required to become expert in using the method. To make the methodology as accessible as possible, we developed an e-learning programme based on our tutorial materials and methods.103 However, we consider that this programme, and 1-day workshops, are good introductions but unlikely, on their own, to bring participants to the level of expertise required for research and implementation. Further, coding BCTs alongside another independent coder will allow discrepancies to be identified and accuracy to be improved.

More widespread use of BCTTv1 is likely to identify ambiguities or uncertainties about labels, definitions and examples, and ways in which they can be improved. Although we are gathering this information where we can via the online training and the study website, we recognise that we require an international consortium to systematically gather and review user feedback, draw in a wider group of users, and oversee the development and refinement of BCTTv2 in a few years. This will include a detailed and transparent log of all changes with their rationales. This approach will allow the international research community to move forward in a co-ordinated fashion, which will maximise communication between groups of users and the efficiency and effectiveness with which new evidence is generated.

As mentioned earlier, there were limitations in the methods used in study 5 that limit our confidence in the findings. We aimed to evaluate BCTTv1 for writing intervention descriptions and used a variety of study designs to do this, gathering data from training workshops. We decided to show participants the intervention in video form so that we did not cue them with the written word. However, taking in detailed information about an intervention by watching an intervention is not something participants were experienced in doing. Additionally, the time pressure of the workshops meant that the videos were very brief and there was not time to show them more than once (which many participants requested). In retrospect, this experimental paradigm was probably too artificial and implemented too hastily for it to have been a good basis for the evaluation. Intervention descriptions usually emerge from reading and discussions, and a better evaluation would be to investigate the impact on this process of using BCTTv1. Given the challenge of control conditions, it is likely that future studies will seek to involve large groups of naive participants, that is those who are new to designing BCIs (e.g. students). An alternative approach, as mentioned earlier, would be to investigate intervention description enhancement than intervention descriptions de novo.

Implications for using Behaviour Change Technique Taxonomy version 1 in evidence synthesis and primary studies

Although BCTTv1 provides a means of characterising intervention content to facilitate intervention implementation, delivery and evaluation, and it is also useful for synthesising evidence. It allows both intervention and control conditions to be coded in terms of BCTs which allows the identification of the BCTs that were used in the intervention over and above those used in the control or usual-care conditions. For example, de Bruin et al.162 found that by coding control conditions, it was possible not only to explain differences in outcomes between conditions but it was also possible to explain variation in outcomes in control conditions. The key point here is that many active controls such as ‘usual care’ involve implementation of multiple BCTs, overlapping with those that constitute the intervention itself.

Behaviour change technique methodology is a starting point for investigating the effectiveness of single BCTs and the combinations of BCTs that typically characterise interventions in evidence synthesis. It is also a starting point for investigating how other factors, such as mode of delivery, intervention intensity, target behaviour, target population and context, may make BCTs more or less effective.163165 However, given the typically small number of studies that have used any particular BCT and potential influence of confounders, there are limits to this methodology. Meta-analyses lack power to test the effectiveness of most BCTs, as was evident in the National Institute for Health and Care Excellence (NICE) 2014 Behaviour Change guidance which used BCT methodology.166 Therefore, it is important to be careful not to conclude that a BCT is ineffective when the conclusion should be that there is insufficient evidence to test for effectiveness. However, the importance of BCT methodology for advancing the field is reflected in the research recommendations within NICE’s Behaviour Change Guidance.167 NICE recommend that research should seek to investigate which combinations of BCTs and which modes of delivery are effective and cost-effective in (1) changing behaviour and (2) in maintaining behaviour change. They recommend seeking to determine how effectiveness varies among people from different sociodemographic backgrounds, those with different skill sets, levels of motivation or with access to different information. Finally, research should include studies that build the evidence base on the effectiveness of each BCT, e.g. using experimental and meta-analytic work to clarify which BCTs work when and for whom.

Investigating behaviour change technique combinations in evidence synthesis and experimental studies

There are several examples of meta-analyses which have investigated both individual BCTs and combinations of BCTs that theory predicts would work synergistically together.21,24,49,168,169 For example, in reviews of interventions to increase physical activity and healthy eating, Michie et al.24 and Dombrowski et al.21 investigated a combination of BCTs predicted by control theory170 and found similar results in two different populations. They found that interventions with the combination of self-monitoring, goal-setting and action planning were twice as effective as those that were not. A similar analytic approach was used to investigate audit and feedback interventions168 in a recent Cochrane review,49 finding that adding the BCTs of goal-setting and action planning to interventions increased the effect of feedback. The theoretically based combination of BCTs associated with provision of information, increasing motivation and enhancing behavioural skills171 has been found to reduce the frequency of sexual interactions that increase health risk.169

An alternative method of combining BCTs is to use CARTs, referred to as Meta-CART,39 to analyse meta-analytic data. This has been used to identify groups of BCTs to predict intervention effects in a reanalysis of data from Michie et al.23 Results showed that providing information about the links between behaviour and health was effective if combined with either setting goals or with providing information on the consequences of the behaviour and using follow-up prompts.

Very brief interventions offer a pragmatic context in which to test whether specific BCTs add to or dilute intervention effectiveness as they tend to include only a small number of BCTs. Such work is being conducted as part of a research programme into very brief interventions to promote physical activity in primary care.172 A similar programme of research, supported by a meta-analysis,173 has identified BCTs in very brief advice interventions to promote smoking cessation.174

With increasingly sophisticated designs, experimental methods can begin to unpack the ‘black box’ of complex interventions. For example, Collins et al.175 have proposed an experimental paradigm, known as the MOST approach (the Multiphase Optimisation Strategy approach) that tests combinations of BCTs as a basis for optimising interventions. Using fractional factorial designs, they advocate selecting combinations of BCTs for testing based on both theory and accumulated evidence. These methods have the advantage that they not only provide evidence of effective combinations, but they also efficiently test theoretical propositions about the synergistic effects of constructs.

Behaviour change techniques and theory

Behaviour change techniques are technologies and in themselves are agnostic with regard to the role of theories. In most cases, there is no attempt to link specific BCTs to theoretical mechanisms. For example, a meta-analysis of 190 interventions to increase physical activity and healthy eating interventions found that 56% of studies claimed the interventions were based on a theory.58 However, 90% of these did not report links between all of the BCTs and specific theoretical constructs.58 When links are made, this is usually the result of the researchers’ judgement rather than being based on evidence, pilot work or a systematic methodology of establishing this. Establishing links between BCTs and theoretical constructs (their mechanisms of action) is a much needed step to advance the science of behaviour change. It is needed to translate theory into intervention design,43,45,161 to explain effective interventions in terms of their theoretical mechanisms,21,24,49,159 to aid practitioners and policy-makers in selecting effective BCTs to target specific behaviours, and to test theory. A large number of theories have been used to explain behaviour change, with a cross-disciplinary review identifying 83.160,176 Just as developing a consensus list of BCT labels and definitions required intensive work to develop a methodology, so developing a consensus about how BCTs link to theoretical mechanisms will require intensive work to develop a methodology. Developing a consensus-based methodology to establish BCT theory links is the aim of a follow-up study to the current BCT study, funded by UK’s MRC (Michie S, Carey R, Johnston M, Rothman A, Kelly M, de Bruin M, et al. University College London, 2015, personal communication). This forms the basis of a larger programme of work, developing a Behaviour Change Ontology identifying the links between five levels of intervention characteristic: target behaviours, BCTs, theoretical mechanisms, modes of delivery and contexts. Given the enormity and complexity of the task, this requires collaboration between behavioural and computer scientists. By using computational machine learning methods of literature interrogation and data mining, it is possible to develop a virtual rapid learning environment to (1) optimise BCIs in the real world and (2) create an updatable open source intervention library for users to identify which combinations of intervention characteristics are most relevant to, and likely to be most effective for, their own behavioural targets and contexts.

Behaviour change techniques, replication and implementation

Given that published reports and existing manuals can effectively be coded into BCTs, there are likely to be benefits of using BCT methodology. These include intervention development, evidence synthesis, assessing and improving the replication of interventions within scientific investigation and the faithful delivery of interventions and treatments in practice. Behavioural interventions to increase fidelity of intervention delivery have the potential to bring about as great, or greater, health gains than medical advances on their own.177 The importance of scientific journals ensuring that intervention content is well specified for replication and implementation has been recognised across the research community.15 At least two journals have editorial policies stating that trials of interventions will only be published if the interventions are described in sufficient detail for replication and implementation, citing BCT methodology as an example.10,178 Guidance by funding bodies would also support the adoption of BCT methodology for specifying and reporting BCIs.

There is ample evidence from reviews and primary studies that intervention protocols are often implemented with insufficient fidelity.12,179182 For example, in an intervention to increase physical activity among sedentary adults at risk of type 2 diabetes mellitus delivered by trained and quality-assured facilitators, 58% of BCTs specified in the intervention protocol were not faithfully delivered.182 This was particularly the case for BCTs directed at maintenance of behaviour change.183 Coding the delivery of BCTs using observations, audio or video recordings, of interventions allows researchers and practitioners to find out how many of the intervention’s proposed active ingredients are actually delivered. Such information can be used to improve the training of those who deliver interventions and their long-term implementation. It also aids the interpretation of trial results, e.g. the extent to which any lack of effects is due to the intervention itself or poor fidelity of delivery. BCTTv1 may also be used to inform the development of measures for assessing delivery of BCTs.31

Behaviour change techniques and designing interventions

Having access to the 93 BCTs of BCTTv1 allows intervention designers to consider a large range of BCTs that might be effective and appropriate for their target behaviour and population. An example of a step-by-step guide for designing BCIs incorporating BCTs is The Behaviour Change Wheel: A Guide to Designing Interventions.161 It links BCTs to intervention functions with the behaviour change wheel framework and to the 14 theoretical domains of the TDF. Intervention designers are encouraged to start their selection of BCTs by conducting a ‘behavioural diagnosis’ of the problem at hand. Because 93 BCTs are likely to be too many to easily work with, we recommend starting with a minimum set composed of the 22 frequently occurring BCTs and/or those shown to be effective in the specific area under investigation. These 22 found to frequently occur in 40 intervention descriptions include 18 of the 22 BCTs including in the Abraham and Michie taxonomy20 based on more than 200 intervention descriptions. Nevertheless, coders in study 4 used 80 BCTs to describe the 40 intervention descriptions and it may therefore be important to expand from the initial 22 BCTs to fully specify the intervention. Another issue is whether or not to use the earlier, shorter taxonomies that have been developed for specific behavioural domains,23,27,29,30 given that these BCTs will have high relevance and include the frequently occurring BCTs for that domain. This needs to be balanced with the potential problem that the scientific study of behaviours sometimes occurs in ‘silos’ so that one may miss potentially effective BCTs that are used in other behaviours. For example, ‘behavioural substitution’ was identified from a systematic review of brief alcohol interventions,29 but this effective BCT had not been identified in several reviews of physical activity, healthy eating and smoking cessation interventions, e.g. Carroll et al.183 A second limitation of sticking with behaviour domain taxonomies is that it limits generalisation of all potential BCTs across behaviours and, therefore, the possibility of generating general models of behaviour change or investigating ways in which BCTs influence different behaviours. Finally, in contrast to earlier taxonomies, BCTTv1 was developed using robust methods and is based on expert consensus, and BCTs in earlier taxonomies (e.g. motivational interviewing) were removed from BCTTv1 as they did not meet the definition of a BCT.

Need for maintenance and updating

The overarching aim of developing BCTTv1 was to maximise the co-ordinated building of evidence and hence the rate at which we can develop more effective BCIs to improve health and well-being, and quality of health care. The aim is to achieve maximum consensus across disciplines, topic areas and countries in order to synthesise and share evidence more efficiently across them. BCTTv1 was termed v1 for a purpose. As BCTTv1 is applied to a wider range of populations, settings and behaviours, adaptations of language and possibly concepts will be needed and new BCTs will be identified. Wider application also involves delivering interventions at different ‘levels’ (e.g. individual, community, organisational, population), as illustrated in Table 18. As BCTTv1 is used to design and specify the content of interventions across wider ranges of delivery modes and contexts, it is likely that additional BCTs will be identified.

TABLE 18

TABLE 18

Different ways of presenting the same BCT

Therefore, we need an international consortium, appropriately resourced, to monitor and collate experiences, adaptations and findings so that BCTTv2 can be developed and released. The timing of this will depend on judgement: balancing the needs for stability and accumulation of evidence using a shared method with the weight of evidence of need for refinement and extension. Discussions are under way with international funding agencies to achieve this.

Final conclusion

The BCTTv1 is a technological advance that represents a step change in the translation of behavioural science into practice and in strengthening the science itself. Like all technologies, its usefulness will be determined by its application and dissemination by researchers, those designing and delivering interventions, funding agencies, journal editors and policy-makers.

Recommendations

The findings from this programme of research point to several recommendations for practice and future research. These are listed below in priority order, starting with the highest priority.

Recommendations for practice:

  • Characterising interventions – to facilitate accuracy, ease and speed of applying BCTTv1 to characterising intervention content, we recommend that users start their coding or other task (e.g. evidence synthesis, reporting interventions) with the list of the 22 most frequent BCTs (see Table 12). If behaviour-specific taxonomies are used, we suggest supplementing them with additional BCTs from BCTTv1.
  • Intervention design – we recommend considering the full range of BCTs in BCTTv1 in the design process, with selection of BCTs guided by theoretical and pragmatic criteria (see the behaviour change wheel guide161).
  • Evidence synthesis – BCTTv1 should be used to specify BCTs in both the active and the control arms of the evaluation trial. The effects of combinations of BCTs can be investigated, e.g. by theoretically informed metaregression and/or Meta-CART analyses.
  • Implementation – to assess and improve implementation (i.e. delivery that is faithful to the protocol), those reporting interventions should specify the content in terms of BCTs and assess delivery, using reliable methodology.

Recommendations for research:

  • Structure of BCTTv1 – a consensus concerning the linkages between BCTs and behaviour change theory is needed to increase BCTTv1’s usefulness for designing theory-based interventions, understanding interventions and testing theory. Work is already under way to address this need (Michie S, Carey R, Johnston M, Rothman A, Kelly M, de Bruin M, et al. University College London, 2015).
  • Reporting interventions – further research is needed to understand the potential usefulness of using BCTTv1 to report BCIs.
  • Understanding effects of BCTs – we recommend that systematic reviews with meta-analyses are developed for each BCT (for those which this has not already been done), starting with the most frequent BCTs.
  • User training – we recommend that further research is needed to evaluate user training, for all 93 BCTs in BCTTv1. This will help to increase understanding as to which BCTs require more/less training and will inform improvement of future training programmes.
  • BCTTv2 – precise documentation of the adaptations of BCTTv1 for specific settings, behaviours and populations is required to inform the development of BCTTv2.
Copyright © Queen’s Printer and Controller of HMSO 2015. This work was produced by Michie et al. under the terms of a commissioning contract issued by the Secretary of State for Health. This issue may be freely reproduced for the purposes of private research and study and extracts (or indeed, the full report) may be included in professional journals provided that suitable acknowledgement is made and the reproduction is not associated with any form of advertising. Applications for commercial reproduction should be addressed to: NIHR Journals Library, National Institute for Health Research, Evaluation, Trials and Studies Coordinating Centre, Alpha House, University of Southampton Science Park, Southampton SO16 7NS, UK.

Included under terms of UK Non-commercial Government License.

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