Name	Info	Provider	Link
	subscription/membership/fee required	Ovid Technologies, Inc.	http://ovidsp.ovid.com/ovidweb.cgi?T=JS&PAGE=linkout&SEARCH=31318012.ui
	free resource	PubMed Central	https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/31318012/
	free resource	Europe PubMed Central	https://europepmc.org/abstract/MED/31318012
	subscription/membership/fee required	Silverchair Information Systems	https://academic.oup.com/aje/article-lookup/doi/10.1093/aje/kwz165
	free resource	Spiral, Imperial College Digital Repository	http://hdl.handle.net/10044/1/71858
Full text from	free resource	White Rose Research Online	https://eprints.whiterose.ac.uk/148346/