Table 2.

Methodological quality of systematic reviews and meta-analyses of the treatment of asthma. Values are number of affirmative answers/number of reviews relevant to each question

Methodological quality (Oxman and Guyatt index16)	All	Cochrane reviews	Peer reviewed journals	P value*	Associated with industry†
Were the search methods used to find evidence on the primary question stated?	33/50	12/12	21/38	<0.005	1/6
Was the search for evidence reasonably comprehensive?	26/33	12/12	14/21	0.032	1/1
Were the criteria used for deciding which studies to include reported?	30/50	12/12	18/38	<0.005	4/6
Was bias in the selection of studies avoided?	15/30	9/12	5/18	0.024	0/4
Were the criteria used for assessing the validity of the included studies reported?	14/50	11/12	3/38	<0.005	1/6
Was the validity of all studies referred to in the text assessed using appropriate criteria?	12/14	9/11	3/3	1.000	1/1
Were the methods used to combine the findings of the relevant studies reported?	26/50	12/12	14/38	<0.005	3/6
Were the findings of the relevant studies combined appropriately?	24/26	11/12	11/14	0.598	4/6
Were the conclusions made by the author(s) supported by the data reported?	25/50	11/12	14/14	<0.005	3/6
Overall quality (median score)‡	3	6	2	<0.005 §	2

^*Fisher's exact test (two tailed) for Cochrane v peer reviewed journals. 

^†These reviews are a subset of the 38 journal reviews. 

^‡The score was obtained by analysing the responses to each of the nine questions, using a standardised set of instructions provided by the developers of the index.⁸ 

^§Wilcoxon rank-sum test (two sided) for Cochrane v peer reviewed journals.