Table 2.

Design features of different kinds of partially clustered trials.

Trial type	Figure reference	Cluster membership exists before randomisation	Level of randomisation	Clustering in all treatment arms	Level of intervention	Alternative names/sub-types of trial designs
Individual randomisation with post-randomisation clustering	2(a)	No	Individual randomisation of observational units	No	Cluster or observational unit	Individually randomised group treatment design; Group-based treatment design; Facilitator/therapist effect design; Partially nested therapist design; Partially crossed therapist design
Individual randomisation within pre-existing clusters	2(b)	Yes	Individual randomisation of observational units	Yes	Observational unit	Re-randomisation design
Cluster randomisation of pre-existing clusters	2(c)	Yes	Cluster randomisation	Yes	Cluster or observational unit	–
Balanced randomisation within pre-existing clusters	2(d)	Yes	Restricted individual randomisation of observational units	Yes	Observational unit	–