Table 5

Number of studies per meta-analysis, overall and broken down by outcome type, intervention comparison type and medical area

Meta-analyses

50%1

75%

90%

99%

Max


All

Total

22453

3

6

10

28

294


Data type

Dichotomous

14886

3

6

10

28

294

Continuous

6672

3

5

8

24

98

Mixed

895

4

7

12

46

133


Medical specialty

Cancer

905

5

8

14

43

69

Cardiovascular

1693

4

7

13

38

58

Central nervous system/musculoskeletal

1965

3

5

8

21

49

Digestive/endocr., nutritional and metabolic

2704

4

6

11

31

138

Gynaecology, pregnancy and birth

4656

3

5

8

20

76

Infectious diseases

965

3

5

9

27

63

Mental health and behavioural conditions

2918

3

5

10

30

174

Pathological conditions, symptoms and signs

701

3

6

10

31

294

Respiratory diseases

3021

3

5

8

20

39

Urogenital

1289

3

5

9

21

31

Other

1636

3

6

10

34

133


Interventions

Pharm. vs. Control/Placebo

8348

3

6

10

30

294

Pharm. vs. Pharm.

5571

3

6

10

28

174

Pharm. vs. Non-Pharm.

424

3

5

11

25

36

Non-Pharm. vs. Control/Placebo

4449

3

5

9

25

61

Non-Pharm. vs. Non-Pharm.

3661

3

5

9

28

58


Outcomes

Signs/symptoms reflecting continuation/end of condition

3639

3

5

9

29

110

Adverse events

2368

3

6

10

26

270

Infection/onset of new acute/chronic disease

2215

3

6

10

24

294

Biological markers

2071

3

6

10

28

138

General physical health

1921

3

5

9

27

58

Obstetric outcomes

1477

3

6

11

24

76

All-cause mortality

1278

4

8

13

36

75

Resource use/hospital stay/process

1187

3

5

9

27

99

Cause-specific mortality/major morbidity event/composite (mortality or morbidity)

920

4

6

11

34

133

Other outcomes (semi-objective)2

2044

3

6

11

30

174

Other outcomes (subjective)3

3239

3

5

9

23

69


1Minimum values and 25th percentiles are not listed, since these were identical across most meta-analysis types. The minimum value was 2 in all rows (noting that meta-analyses needed to contain at least 2 studies to be eligible for inclusion). The 25th percentile was 3 for Cancer and All-cause mortality, and 2 in every other row.

2Other outcomes (semi-objective): External structure, Internal structure, Surgical/device related success/failure, Withdrawals/drop-outs

3Other outcomes (subjective): Pain, Mental health outcomes, Quality of life/functioning, Consumption, Satisfaction with care, Composite (at least 1 non-mortality/morbidity)

Davey et al. BMC Medical Research Methodology 2011 11:160   doi:10.1186/1471-2288-11-160

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