Table 1

Examples of cluster randomised trials of injury interventions

Study	Unit of randomisation	Intervention	Primary outcome(s)	Number of clusters	Average cluster size	Estimated ICC
Bennewith et al 20023	General practices in specified hospital catchment areas	Mailing for GPs about index episode of self-harm in registered patient, guidelines for management	Repeat episodes of self-harm	98 general practices	20 patients per practice	0.006 for repeat episode of deliberate self-harm
Blake et al 20084	Schools	Bicycle helmet curriculum and demonstration, individual fit check and feedback within class	Correct helmet use	12 schools	14 children per school	Not provided
Cox et al 20085	Primary care organisations (PCOs)	Training on fracture prevention; feedback from specialist nurses to staff and GP on each patient's fall risk, with recommendations	All fractures and hip fractures	58 primary care organisations	Four care homes per PCO	0.20 for all fractures 0.21 for hip fracture
Cumming et al 20086	Hospital wards	Targeted multi-factorial intervention (patient risk assessment, education, exercise, bed alarms, and drug review; modification of bedside and ward environment; staff training)	Falls	24 hospital wards	167 patients per ward	0.014 unadjusted 0.003 adjusted for length of stay and previous falls
DiGuiseppi et al 20027	Electoral wards	Door-to-door distribution of smoke alarms	Fire-related injuries	40 electoral wards	3686 households per ward	0.00017 for all preventable injuries, 0.00011 for preventable hospitalisations and death
Kendrick et al 19998	General practices	Safety advice at three child health surveillance consultations; low cost safety equipment to families on means tested state benefits; home safety checks and first aid training by health visitors	Medically attended injuries	36 general practices	55 children per general practice	0.017 for medically attended injury
Kendrick et al 20059	General practices	Training for midwives and health visitors; educational package delivered by midwives and health visitors to parents to reduce baby walker possession and use	Self-reported possession and use of baby walker	64 general practices	16 mothers per practice	0.053 for possession of baby walker 0.050 for use of baby walker
Kendrick et al 200710	Schools	‘Risk Watch’ programme delivered by teachers as classroom curriculum (safety); teachers trained and provided with materials	Safety knowledge	20 schools	23 schoolchildren per school	Knowledge scores: ICC for fire and burn prevention 0.187, poisoning prevention 0.097, bike and pedestrian safety 0.072, falls prevention 0.234
Mulvaney et al 200611	Schools	Reflective visibility aids, educational booklet, parent letter; usual road safety education	Wearing of visibility aids	20 school classes (one per school)	19 children per class	0.45 for any visibility aid at 1 week after intervention, 0.21 at 8 weeks
Olsen et al 200512	Handball sports clubs	A structured warm-up programme to improve running, cutting, and landing technique as well as neuromuscular control, balance, and strength	Acute injury to the knee or ankle	120 clubs	15 players per club	0.057 for acute injury to the knee or ankle, 0.043 for all injuries

GP, general practitioner; ICC, intraclass correlation coefficient.