“With streaming, it’s really a different model today,” said Jennifer Kent, who conducts market research on consumer habits with consulting firm Parks Associates. “A lot of the audience isn’t watching a same title at the same time. You might be watching a title on your mobile phone or on this smart TV, and then this other TV in your household is actually an Amazon Fire Stick.”
Kent said that fragmentation has made it hard for a third party like Nielsen to accurately track streaming data.
From the article, "WGA contract pushes for more transparency around streaming data" by Meghan McCarty Carino