Authors of stepped or phased approaches to intervention development start by describing how a problem has been identified. The existence of a problem may be identified from published evidence synthesis, clinical practice, political strategy or needs assessment . Alternatively, researchers or practitioners may have worked in a field for many years and identified the need for a new intervention . In a clinical setting, the clinical significance of the problem, and the ability to make a clinically significant difference, is identified as the driver for selection of problems in need of a new intervention .
2. Establish a group or set of groups to guide the development process, thinking about engagement of relevant stakeholders such as the public, patients, practitioners and policy makers [27, 31, 34, 39,40,41, 53, 54]
Authors of a range of categories of intervention development explicitly consider the number, membership and role of groups that need to be established and run throughout the whole development process. Some authors recommend that a group is established that has ‘editorial rights’ (that is, makes final decisions about the intervention) and other groups are established that may deliver any technical expertise needed or offer advice and expertise for decision-making . The ‘editorial rights’ group—sometimes called ‘the development team’—includes the developers and, in some approaches, includes members of the target population at which the intervention is aimed and practitioners likely to deliver it. Authors of user-centred approaches recommend including a variety of disciplines and expertise in this development team to generate innovation [33, 43]. Authors of stepped or phased approaches also recommend diverse membership to facilitate the development process, e.g. include people with computer science skills when designing digital interventions [34, 53].
In partnership approaches, the development team includes a diverse range of stakeholders, particularly members of the target population, who are equal partners with other team members, that is, have editorial rights [39, 40]. Those leading the intervention development will make efforts to encourage engagement of members of the target population, especially of hard-to-reach groups, develop inclusive communication processes for the group, and consider the assets (knowledge, experience, skills and abilities, influence and connections) available within the group . This focus on bringing a variety of stakeholders together, and collaborative working with the target population and those who will deliver the intervention, is not unique to partnership approaches. Authors of some theory and evidence based approaches value this, working with a ‘planning group’ throughout the process, and seeking consensus after open discussion of diverse views . Membership of these groups may change over time as the intervention, its target population, and who will deliver it become clear . However, a unique aspect of partnership approaches is that members of the target population have decision-making rights throughout the development process.
3. Understand the problems or issues to be addressed
Different authors address this action in different ways (see below). For partnership and target population-based approaches the focus is on in-depth understanding of the target population and the context in which the intervention will be delivered. For theory and evidence-based approaches this understanding is gained from theory and published research. Some approaches include both of these strategies but may place different weights on them. There are five sub-actions (i)-(v).
(i) Understand the experiences, perspectives and psycho-social context of the potential target population
The target population may be clients, patients, staff or a combination of these. This can involve identifying the priorities and needs of the potential target population, what matters most to people rather than what is the matter with them, why people behave as they do and understanding the lived experience of the potential target population [17, 25, 27, 30, 33, 34, 39,40,41,42, 44, 45, 53, 54, 56]
Some authors highlight this as the first action in the process and one that shapes the whole process [30, 33]. It is central to partnership and target population centred approaches where understanding the lived experiences and needs of the target population is the basis of the intervention. Secondary and primary qualitative research is recommended: synthesis of qualitative research; iterative qualitative research using diverse samples and open questions to explore people’s experiences and needs; use of patients’ narratives or archives of patient experiences and observation; consultation with stakeholders; and use of patient and public involvement [17, 41, 42]. Use of observation or ‘shadowing’ patients and families is recommended as well as obtaining the views of the target population because people may not be able to articulate the problem fully [33, 40]. Theory and evidence-based approaches, and stepped or phased approaches, also make use of qualitative research with the target population, including observation [27, 34].
(ii) Assess the causes of the problems
Authors of a range of approaches recommend the use of the evidence base through literature or systematic reviews [24, 29, 34]. Alternatives are drawing a logic model of the problem or model of causal pathways [27, 28] and creative approaches, such as group discussions, as a way of developing questions for research evidence reviews .
(iii) Describe and understand the wider context of the target population and the context in which the intervention will be implemented
This sub-action can be undertaken as part of the earlier sub-actions (i) and (ii) but some approaches emphasise the importance of understanding context and so it is described as a separate action here. Bartholomew specifies the contexts of population, setting and community . Again, the use of qualitative research, particularly observation, is recommended. The observation may be of service delivery where the intervention will occur [41, 42] or of the target population in their real life context [33, 43,44,45]. Conducting an asset assessment, that is, determining the strengths of the community in which an intervention will take place is useful for a health promotion intervention . Some theories can help to understand important aspects of context for implementation of the intervention in the real world .
(iv) Identify evidence of effectiveness of interventions for these problems, or for similar interventions once decisions have been made about the intervention type, so do not reinvent the wheel.
A range of approaches recommend systematic reviews of quantitative evidence of effectiveness of interventions to identify what has worked, and qualitative evidence to understand why interventions have worked or not [7, 17, 31].
Authors of partnership and stepped/phased approaches recommend working with wider stakeholders such as policy makers, community leaders or service providers to clarify and understand the problems. This can involve using research methods to obtain their views, meetings to facilitate communication, or equal partnership with stakeholders using activities to encourage active engagement in the context of partnership approaches. Wider stakeholders may already be fully engaged within partnership approaches or because they are members of groups established in Action 2.
5. Identify possible ways of making changes to address the problems.
This involves identifying what needs to change, how to bring about this change and what might need to change at individual, interpersonal, organisational, community or societal levels [7, 17, 26, 27, 29, 30, 34, 48, 55]
This action is addressed differently depending on the category of approach, and aim and context, of the intervention. Interventions aiming to address behaviour change in public health specify this action in detail, recommending the creation of a ‘logic model for change’ showing mechanisms of change and causal relationships between theory and evidence-based change methods [27, 28]. The emphasis is on drawing on existing theory or theories, and the research evidence base, to link determinants of a problem and the objectives of the intervention . Identifying a variety of theories rather than a single theory, including theories relevant to later parts of the development process, e.g. implementation theory, is recommended  at this action.
Other approaches offer less detail about how to do this but suggest drawing a ‘conceptual map’  or point out that it should be influenced by the earlier qualitative research with stakeholders, including the target population and those who will deliver intervention . Qualitative research can be used to ask why people would make any proposed changes, how change should occur and barrier and facilitators to change.
6. Specify who will change, how and when.
Authors of theory and evidence-based approaches detail this action, recommending using the combination of a theory or theoretical framework with data from multiple sources such as interviews, focus groups, questionnaires, direct observation, review of relevant documents, literature and involvement of stakeholders such as staff or patients . There may be a long list of issues to change and these will need to be prioritised at this action .
Understanding the context (see Action 3.iii above) can help here. Authors recommend considering wider issues such as the cost of an intervention or the stigma attached to using it  or how it fits with current expectations of a professional group that would deliver it . This is a key action for implementation-based approaches. The authors of  recommend consideration of the barriers to reaching the target population, how the intervention will function for different sub-groups, what percentage of organisations would be willing to adopt the intervention when tested and ability to overcome any barriers . This thinking and planning occurs early in the process and can involve formative research with wider stakeholders. Authors of a range of other approaches propose that implementation is considered at this early stage [24, 29], with the use of theory to facilitate understanding of this  and the need to keep implementation issues in mind throughout later processes . Issues other than effectiveness and cost-effectiveness that are related to implementation can be considered: affordability, practicability, acceptability, safety and equity . Authors of partnership approaches recommend bringing staff and patients together to increase engagement and improve implementation . Authors of stepped or phased approaches recommend that developers have to understand the real world of practice so they can develop not only effective interventions but interventions that practitioners adopt .
The cost of delivering an intervention may outweigh the benefits it can potentially achieve. This issue is addressed in economic modelling undertaken alongside RCTs but can also be considered at the planning step by modelling processes and outcomes to determine if it is worth developing an intervention . Alternatively, if solutions to barriers to future implementation in the real world (see Action 7) cannot be found then it might not be worth developing an intervention .