Name	Info	Provider	Link
	subscription/membership/fee required	Ingenta plc	https://www.ingentaconnect.com/openurl?genre=article&issn=&volume=67&issue=1&spage=18&aulast=Langenfeld
	subscription/membership/fee required	Ovid Technologies, Inc.	http://ovidsp.ovid.com/ovidweb.cgi?T=JS&PAGE=linkout&SEARCH=37647138.ui
	subscription/membership/fee required	Wolters Kluwer	https://doi.org/10.1097/DCR.0000000000003057