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

Table 6 Study sample size, overall and broken down by outcome type, intervention comparison type and medical area

		Studies	25%	50%	75%	Max
All	Total	112600	44	91	210	1242071
Data type	Dichotomous	77237	50	102	243	1242071
	Continuous	29902	33	62	142	18851
	Mixed	5461	21	86	251	36511
Medical specialty	Cancer	6441	72	154	326	266064
	Cardiovascular	10686	44	102	289	67800
	Central nervous system/musculoskeletal	8299	43	80	149	9440
	Digestive/endocr., nutritional and metabolic	15345	42	79	160	18819
	Gynaecology, pregnancy and birth	20098	60	118	293	23697
	Infectious diseases	4502	59	130	371	419748
	Mental health and behavioural conditions	15218	36	63	165	9020
	Pathological conditions, symptoms and signs	4448	40	61	115	2463
	Respiratory diseases	13153	36	87	227	82892
	Urogenital	5914	39	71	153	4912
	Other	8496	44	90	198	1242071
Interventions	Pharm. vs. Control/Placebo	44156	41	90	222	58050
	Pharm. vs. Pharm.	28018	48	99	222	25180
	Pharm. vs. Non-Pharm.	2018	50	74	135	7711
	Non-Pharm. vs. Control/Placebo	20892	41	92	229	1242071
	Non-Pharm. vs. Non-Pharm.	17516	45	85	169	82892
Outcomes	Signs/symptoms reflecting continuation/end of condition	17621	42	83	197	359600
	Adverse events	11898	49	100	242	82892
	Infection/onset of new acute/chronic disease	11284	56	110	258	1242071
	Biological markers	10578	35	64	147	266064
	General physical health	8959	30	66	177	131271
	Obstetric outcomes	7376	60	117	293	18453
	All-cause mortality	8302	52	110	281	259627
	Resource use/hospital stay/process	5454	50	98	200	419748
	Cause-specific mortality/major morbidity event/composite (mortality or morbidity)	5413	69	165	449	266064
	Other outcomes (semi-objective)¹	10886	44	81	177	131271
	Other outcomes (subjective)²	14490	38	71	162	359600

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