Table 1.

Some reviews of published cluster randomised trials

Authors	Source of trials	Years	Clustering allowed for in sample size	Clustering allowed for in analysis
Donner et al. [8]	16 non-therapeutic intervention trials	1979 – 1989	<20%	<50%
Simpson et al. [9]	21 trials from American Journal of Public Health and Preventive Medicine	1990 – 1993	19%	57%
Isaakidis and Ioannidis [11]	51 trials in Sub-Saharan Africa	1973 – 2001 (half post 1995)	20%	37%
Puffer et al. [10]	36 trials in British Medical Journal, Lancet, and New England Journal of Medicine	1997 – 2002	56%	92% a
Eldridge et al. [12]	152 trials in primary health care	1997 – 2000	9%	59%
Varnell et al. [13]	60 trials in American Journal of Public Health and Preventive Medicine	1998 – 2002	20%	54% (all analyses) + 25% (some analyses only)

^a My review of trials identified by Puffer et al. [10]