Association of Metformin Use with Asthma Exacerbation in Patients with Concurrent Asthma and Diabetes: A Systematic Review and Meta-Analysis of Observational Studies

Table 2

Risk of bias of included cohort studies.

	Selection				Comparability		Outcome
	(1) Representativeness of the exposed cohort	(2) Selection of the nonexposed cohort	(3) Ascertainment of exposure	(4) Demonstration that outcome of interest was not present at start of study	(1) Comparability of cohorts on the basis of the design or analysis	(1) Assessment of outcome	(2) Was follow-up long enough for outcomes to occur?	3) Adequacy of follow-up of cohorts
Li [11]	1	1	1	1	1	1	1	1
Wu [12]	1	1	1	1	1	1	1	1

Primary outcomes are given.