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Table 5 Number of studies per meta-analysis, overall and broken down by outcome type, intervention comparison type and medical area

From: Characteristics of meta-analyses and their component studies in the Cochrane Database of Systematic Reviews: a cross-sectional, descriptive analysis

   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
  1. 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.
  2. 2Other outcomes (semi-objective): External structure, Internal structure, Surgical/device related success/failure, Withdrawals/drop-outs
  3. 3Other outcomes (subjective): Pain, Mental health outcomes, Quality of life/functioning, Consumption, Satisfaction with care, Composite (at least 1 non-mortality/morbidity)