About: http://webisa.webdatacommons.org/11298418

Property	Value
http://www.w3.org/1999/02/22-rdf-syntax-ns#type	http://www.w3.org/ns/prov#Entity
http://www.w3.org/ns/prov#value	inherent to case-control studies, described as early as 1959 [13], is the difficulty to ensure that cases and controls are a representative sample of the same source population.
http://www.w3.org/ns/prov#wasQuotedFrom	nih.gov