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Table 1 Characteristics of cluster randomised controlled trials published in the NIHR Journals Library, from 1 January 1997 to 15 July 2021

From: Statistical analysis of publicly funded cluster randomised controlled trials: a review of the National Institute for Health Research Journals Library

Characteristic n %
NIHR journal the cRCT was reported in (N = 79+)
 HTA 38 48
 PHR 14 18
 HSDR 5 6
 PGAR 22 28
 EME 0 0
Trial design (N = 86)
 Parallel 73 85
 Factorial 7 8
 Cross-over 2 2
 Others* 4 5
Number of trial arms (N = 86)
 2 69 80
 3 10 12
 2 × 2 4 5
 2 × 2 × 2 2 2
 2 × 6 1 1
Clinical area (N = 86)
 Cancer/oncology 8 9
 Mental health (including neurosciences/psychiatry/psychology/dementia) 21 25
 Orthopaedics/rheumatology/musculoskeletal (including back pain) 2 2
 Obstetrics and gynaecology 2 2
 Primary care 6 7
 Cardiovascular 1 1
 Gastrointestinal 2 2
 Respiratory 1 1
 Stroke 4 5
 Diabetes 6 7
 Dermatology (including ulcers) 1 1
 Others† 32 37
Setting (N = 86)
 Hospital 4 5
 General practice 25 29
 Mixed 3 3
 Community 3 3
 Others‡ 51 59
Level of clustering (N = 86)
 2 85 99
 3 1 1
Trial registration (N = 86)
 ISRCTN 78 91
 NTC 2 2
 Not reported 6 7
Type of intervention (N = 86)
 Therapy 8 9
 Behaviour change technique 4 5
 Complex intervention 17 20
 Education 12 14
 Exercise 3 3
 Information and communication technology 3 3
 Medical device 2 2
 Screening 2 2
 Training 17 20
 Others§ 18 21
Type of control (N = 86)
 Active 86 100
Are patient blinded (N = 86)
 Yes 8 9
 No 78 91
Any form of a pilot studya (N = 86)
 Yes 72 84
 No 14 16
Geographical region (N = 86)
 Multiple regions 54 63
 Regional 32 37
  1. aThese are internal pilot studies carried out within the main trials; they are different from the external pilot/feasibility studies mentioned initially in text
  2. +79, the total number of journal reports included, which reported the results of 86 cRCTs (79 reports included the results of 86 cRCTs)
  3. *Partial factorial and step-wedged trials
  4. †Insomnia, paediatrics, youth bullying and other aggressive behaviours, traumatic brain injury, autism spectrum disorders, prehospital emergency care, obesity, epilepsy, oral health, end of life care, children fruit and vegetable intake, alcohol abuse, physical activity, psychosocial work environments, relationship and sexuality education, illicit drug use, smoking prevention, social and emotional wellbeing of children, dating and relationship violence, emergency admission to hospital, care for older people, multimorbidity, abdominal surgery, care of people with long-term conditions, care planning in secondary care mental health services and psychosis, eating disorder, injuries in under-fives children, patient involvement in safety, psychosis, care planning in secondary care mental health services
  5. ‡Care homes, nursing homes, clinics, NHS trust, residential services, stroke rehab unit, children centre, paediatrics diabetes clinic, schools, ambulances services, dental practice, stroke services
  6. §Telephone triage, strategies to increase screening, financial incentive, invitation letter, leaflet, behavioural approaches, questionnaire, redesigned care model, health promotion, operational protocol, implementation package, time
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