Conceptual decomposition of complex health care interventions for evidence synthesis: a literature review

RATIONALE, AIMS AND OBJECTIVES: The clarity of pivotal concepts is an important prerequisite for the development, evaluation and exchange of scientific ideas. The term 'complex intervention' is increasingly used in the health care literature, although it often remains unclear what is actually meant by this concept. Therefore, our aim was to analyse the literature regarding definitions of the terms 'complex intervention' and 'components' of such interventions. METHOD: To identify the methodological publications, systematic and snowballing techniques were combined for the literature search. Relevant units of meaning were extracted from 68 included publications. Afterwards, we deduced categories and related frequencies by inductive and quantitative content analysis techniques. RESULTS: Several types of complexity were distinguished in the literature. Most authors viewed complex interventions as multicomponent interventions that are characterized by interactions between the components themselves, with the context or as systemic interventions. Components of complex interventions were described in the publications as having the potential to causally influence outcomes, thus being essential for achieving an effect. Other definitions and inconsistencies among the definitions are highlighted and discussed. CONCLUSIONS: From our synthesis, we derived definitions of the central health care-related concepts 'complex intervention' and 'components' of an intervention. Although we found numerous diverse definitions, they could be reduced to a defined number of core characteristics. These characteristics may facilitate communication regarding complex interventions and enable the deduction of methodological approaches for evidence synthesis.