Stanford University Metadata Study: Lots of Personal Information Revealed

Jonathan Mayer, a graduate student leading the project, wrote...

“We did not anticipate finding much evidence one way or the other, however, since the MetaPhone participant population is small, and participants only provide a few months of phone activity on average. We were wrong. We found that phone metadata is unambiguously sensitive, even in a small population and over a short time window. We were able to infer medical conditions, firearm ownership, and more, using solely phone metadata.”

The 'more" include a likely abortion, preparations to grow illegal drugs, and relapsing multiple sclerosis.

Indiana University law professor Fred Cate is quoted as saying of the study:

“It highlights three key points. First, that the key part of the NSA’s argument—we weren’t collecting sensitive information so what is the bother?—is factually wrong. Second, that the NSA and the [Foreign Intelligence Surveillance Act] Court failed to think this through; after all, it only takes a little common sense to realize that sweeping up all numbers called will inevitably reveal sensitive information. Of course the record of every call made and received is going to implicate privacy. And third, it lays bare the fallacy of the Supreme Court’s mind-numbingly broad wording of the third-party doctrine in an age of big data: just because I reveal data for one purpose—to make a phone call—does not mean that I have no legitimate interest in that information, especially when combined with other data points about me.”

More here, here, and here.

My question: If large amounts of sensitive data are not revealed by metadata searches, why would the NSA perform metadata searches?