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Table 3 The complexity spectrum

From: Intervention description is not enough: evidence from an in-depth multiple case study on the untold role and impact of context in randomised controlled trials of seven complex interventions

Characteristic Simple Highly complex
1. Number of components within intervention One for example, single drug Several for example, rehabilitation package
2. ‘Dose’ or intensity of intervention Pre-determined/uniform for example, specified dose drug or pre-prepared information leaflet Dependent on characteristics or participation of individual for example, exercise intervention
3. Clarity re the components of the intervention Clearly defined components delivered in a specified order for example, diagnostic procedure Less well-defined components not delivered in a particular order for example, behavioural intervention
4. Degree of confidence in the ‘active ingredient’ Known ‘active ingredient’ for example, specific medication Unknown active ingredient even if components are known for example, smoking cessation activity
5. Timing of intervention Single event for example, one-off procedure Protracted intervention or multiple time points for example, follow-up care
6. Number of people involved in delivery One Several
7. Clarity of responsibility in intervention Clearly defined Ill-defined
8. Number of professional groups involved One Several
9. Technical or professional skill involved Minimal skill for example, sending information by post Highly skilled for example, surgical procedure
10. Human interaction required to deliver the intervention Little for example, dispensing of a medication Intervention is dependent on human interaction for example, counselling
11. Setting Single well-defined setting for example, single therapy room Cross boundary or multiple settings for example, hospital at home scheme
12. Level of patient involvement or active participation Low for example, radiotherapy treatment High for example, self-care intervention or group activity
13. Sphere of impact Narrow for example, influences individual patients but no impact on or involvement of rest of service Broad for example, service development intervention with implications for entire service
14. Clarity of main outcome Clear and obvious outcome for example, cessation of smoking, length of stay following early discharge Ambiguous outcome(s) for example, improvement in quality of life or patient satisfaction, multiple outcomes that are all important