Table 1.

Overview of CReDECI

No	Item	Explanation
First phase – Development
1	Description of the intervention’s underlying theoretical considerations	The theoretical basis of the intervention should be clearly stated. This includes the theory on which the intervention is founded as well as, if available, empirical evidence from studies in different settings or countries.
2	Description of all components of the intervention	Complex interventions contain several interacting components, which make up the intervention. All components should be clearly specified. A graphical presentation of the components might be useful.
3	Rationale for the selection of the intervention’s components	A description of the rationale for choosing the selected components should be given. If formerly successfully proven components have been excluded from the intervention, the rationale should be stated.
4	Illustration of any intended interactions between different components	In some cases different components are designed to support or to enhance the effect of other components. All expected reciprocal effects should be explained.
5	Rationale for the aim/essential functions of the intervention’s components, including the evidence whether the components are appropriate for achieving this goal	It is necessary to describe the aim or essential function of the intervention’s components rather than the content in detail, e.g. the content of an education programme may differ more between various countries than the aim or essential function.
6	Consideration of contextual factors and determinants of the setting in the modelling of the intervention	The intervention should be tailored to the target setting. This includes legal or political issues of a country as well as local conditions of the participating centres.
Second phase – Feasibility and piloting
7	Information on pilot-testing	The intervention should have been pilot-tested in order to determine feasibility, acceptability, and practicability of the complex intervention. The pilot test should take into account the key uncertainties which have been identified during the development process.
8	In case of pilot-test: presentation of all relevant results and their impact on the modelling of the final intervention	Results of the pilot test and any subsequent modification of the intervention are highly relevant for other researchers in the field and should be published.
Third phase – Introduction of the intervention and evaluation
9	Description of the control intervention (comparator)	Information on the characteristics of the control intervention (e.g. usual care or optimised usual care) should be given. It should be stated whether components of the intervention were accessible for the control group, whether a specific control intervention was delivered, or whether the control group did not receive any intervention. If the study took place in different centres, differences in usual care across centres should also be described.
10	If the study was conducted in different clusters or centres: description of a standardised implementation strategy throughout the centres	The implementation strategy should include methods to deal with the local conditions, e.g. education of persons in charge for the implementation, and methods to adjust the implementation process in order to maintain a standardised implementation of the intervention.
11	Description of all materials or tools used for the implementation of the intervention to allow a replication of the study	Complex interventions often comprise materials, e.g. brochures, checklists or flyers. These materials might influence the interventions’ effects and should be publicly accessible. In addition, the use of incentives may influence study adherence and should therefore be stated.
12	Description of an evaluation of the implementation process	Process evaluation is a prerequisite for determining the success of the intervention’s implementation and should be an integral part of the intervention’s evaluation.
13	Description of any deviation from the study protocol during the implementation process	In order to replicate the study, information on the actual delivery of the intervention and on any deviation from the study protocol concerning the implementation should be reported. Deviations and necessary adjustments of single components or the whole intervention during the implementation process should be published. Adjustments may have been necessary for a single centre, several clusters or the whole intervention group.
14	Description of facilitators or barriers revealed by the process evaluation which have influenced the interventions’ implementation	Any facilitators or barriers identified in the context of the process evaluation should be described. Information on facilitators or barriers may be derived both from staff and from the research team. Any interpretation of facilitators or barriers, e.g. in the discussion section of the publication, should be clearly separated in (1) information collected during the process evaluation and (2) information derived from other studies.
15	Description of unexpected interactions between components of the intervention and the environment in which the intervention was implemented	It should be stated if any change had been observed which may have been caused by the implementation of the intervention.
16	Description of costs or required resources for the intervention’s implementation	Information on costs or required resources necessary to implement the intervention should be available in the publication or as reference to an economic evaluation. Resources should include all expenses necessary for the intervention’s implementation, e.g. personnel costs, material or equipment.