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	A [label="PubMed (n=39)
Google Scholar (n=409)
arXiv (n=105)" fillcolor=gray95]
	B [label="Articles identified
through database
searching
(n=553)" fillcolor=gray98]
	C [label="Articles after content
screening and
duplicate removal
(n=105) " fillcolor=gray98]
	D [label="Articles included in
the analysis
(n=154)" fillcolor=gray98]
	E [label="Additional articles
identified through
bibliography search
(n=49)" fillcolor=gray98]
	B -> C
	C -> D
	E -> D
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