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5.3  Defining types of interventions: which comparisons to make?

The second key component of a well-formulated question is to specify the interventions of interest and the interventions against which these will be compared (comparisons). In particular, are the interventions to be compared with an inactive control intervention (e.g. placebo, no treatment, standard care, or a waiting list control), or with an active control intervention (e.g. a different variant of the same intervention, a different drug, a different kind of therapy)?


When specifying drug interventions, factors such as the drug preparation, route of administration, dose, duration, and frequency should be considered. For more complex interventions (such as educational or behavioural interventions), the common or core features of the interventions will need to be defined. In general, it is useful to consider exactly what is delivered, at what intensity, how often it is delivered, who delivers it, and whether people involved in delivery of the intervention need to be trained. Review authors should also consider whether variation in the intervention (i.e. based on dosage/intensity, mode of delivery, frequency, duration etc) is so great that it would have substantially different effects on the participants and outcomes of interest, and hence may be important to restrict.


Box 5.3.a outlines some factors to consider when developing criteria for the ‘Types of interventions’ (and comparisons).