Are there any studies that show whether cross-site user tracking actually increases ad click-through rates? An advertiser can already intuit a lot about a reade

Are there any studies that show whether cross-site user tracking actually increases ad click-through rates? An advertiser can already intuit a lot about a reader from the current web site or search terms without tracking their activity on other sites. The most relevant ads I've seen were from Feedly and Twitter, who have their own profiles based on RSS feeds or Twitter accounts I follow.