Name	Info	Provider	Link
	free resource	PubMed Central	https://www.ncbi.nlm.nih.gov/pmc/articles/pmid/30976253/
	subscription/membership/fee required	Springer	https://link.springer.com/article/10.1007/s10680-017-9439-z
	free resource	Europe PubMed Central	https://europepmc.org/abstract/MED/30976253