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Improving understanding of intervention complexity: the Intervention Complexity Assessment Tool for Systematic Reviews (iCAT_SR)

Date and Location




Friday 20 September 2013 - 15:30 - 17:00


Presenting author and contact person

Presenting author

Simon Lewin

Contact person

Maggie Hendry
Jackie Chandler
Andy Oxman
Abstract text
Background Health care interventions fall along a spectrum from simple to more complex. There is growing interest in methods for reviewing ‘ complex interventions’, but little work has been conducted on how to assess intervention complexity in the context of systematic reviews. Such assessments may assist review authors in: systematically describing interventions; grouping interventions; planning sub-group analyses; identifying causal pathways; and developing logic models. Objectives To describe a new tool (iCAT_SR) to assess the complexity of interventions in the context of systematic reviews. Methods iCAT_SR was developed by adapting and extending an existing complexity assessment tool (Lewin 2006). Adaptation was done through workshops with review authors and implementation researchers; review of relevant literature; and testing the tool against published reports of interventions. Results The tool comprises ten dimensions: the number of active components in the intervention; the number of behaviours of recipients to which the intervention is directed; the range of organizational levels targeted by the intervention; the degree of tailoring intended across sites or individuals in intervention application; the level of skill required by those delivering the intervention; the level of skill required by those receiving the intervention; the degree of interaction between intervention components; the degree to which the effects of the intervention are context dependent; the degree to which the effects of the interventions are modified by recipient, provider or implementation factors; and the length of the causal pathway between intervention and outcome. Dimensions 1–6 are considered “core” dimensions. Dimensions 7–10 are optional; they may not be useful for all interventions and may be more difficult to apply. Conclusions The detailed disaggregation of the components of interventions included in a systematic review, using the iCAT_SR complexity assessment tool, will assist in understanding the comparisons made and interpreting review findings.