Table 1 Characteristics of the 51 included trials

Study design

   Parallel

49 (96)

   Factorial

2 (4)

Number of arms

   2 arms

38 (75)

   3 arms

8 (16)

   4 arms

2 (4)

   5 arms

3 (6)

No. of participants

   Total number of participants in all trials

48,323

Mean number of participants per trial

(excluding outlier involving 14,802 participants)

670

   Median number of participants per trial (IQR)

457 (212 to 806)

Trials achieving sample size

   Trials achieving at least required sample size

18 (35%)

   Trials recruiting 80% of original target

34 (67%)

Intervention evaluated

   Service Delivery

11 (22)

   Surgery

8 (16)

   Psychological Therapy

5 (10)

   Physical Therapies

5 (10)

   Diagnostic

5 (10)

   Drug

4 (8)

   Devices

4 (8)

   Social Care

3 (6)

   Education and Training

2 (4)

   Complementary Therapies

2 (4)

   Vaccines and Biologicals

1 (2)

   Diet

1 (2)

Disease (ICD10 chapter)

M00-M99 Diseases of the musculoskeletal system and

connective tissue

8 (16)

G00-G99 Diseases of the nervous system

8 (16)

I00-I99 Diseases of the circulatory system

8 (16)

Z00-Z99 Factors influencing health status and contact with

health services

6 (12)

F00-F99 Mental and behavioural disorders

6 (12)

O00-O99 Pregnancy, childbirth and the puerperium

4 (8)

K00-K93 Diseases of the digestive system

3 (6)

N00-N99 Diseases of the genitourinary system,

3 (6)

C00-D48 Neoplasms

2 (4)

LOO-L99 Diseases of the skin and subcutaneous tissue

1 (2)

P00-P96 Certain conditions originating in the perinatal

Period

1 (2)

S00-T98 Injury, poisoning and certain other consequences

of external causes

1 (2)

Primary outcome types in the 51 trials*

   Symptom score or measurement of depression/pain

13 (25)

   Quality of life measure (including generic and disease specific)

10 (19)

   Positive event rate (e.g. improvement in symptoms)

10 (19)

   Adverse event rate (e.g. post operative nausea and vomiting)

9 (17)

   Survival/mortality

6 (11)

   Measurement of function

4 (8)

   Other

1 (2)

Intention to treat analysis

   Yes

48 (94)

   No

0 (0)

   Unclear

3 (6)

Blinding / Masking

   Participant blinded

2 (4)

   Outcome assessor blinded

13 (25)

   Person administering intervention blinded

1 (2)

   No blinding

38 (74)

Combination of blinding / masking

   Participant and outcome assessor blinded only

2 (4)

   Administrator and outcome assessor blinded only

1 (2)

   Outcome assessor blinded only

10 (20)

   No blinding

38 (74)