Alterations in short-chain fatty acids and serotonin in irritable bowel syndrome: a systematic review and meta-analysis

Table 8 Quality assessment of the included studies

References	Year	Selection	Comparability	Exposure	Total
Ringel-Kulka et al. [26]	2015	4	1	2	7
Tana et al. [25]	2010	4	1	2	7
Kopecny and Simunek [27]	2002	2	1	2	5
Vernia et al. [28]	1987	2	1	2	5
Mortensen et al. [8]	1987	2	1	2	5
Yu et al. [30]	2016	2	1	2	5
Dunlop et al. [31]	2005	4	1	2	7
Thijssen et al. [32]	2015	4	1	2	7
Park et al. [29]	2009	4	1	2	7
Keszthelyi et al. [33]	2013	4	1	2	7

Selection includes four criteria: (1) is the determination of case adequate? (2) the representation of the cases, (3) the selection of the controls, (4) The determination of the controls; Comparability criteria include the Comparability of cases and controls is taken into account in design and statistical analysis; Exposure contains three criteria: (1) determination of exposure factors, (2) use the same method to determine the exposure factors in case and control group, (3) non-response rate

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