Assisting Robertson in his discovery was computer scientist Latanya Sweeney, professor of government and technology in residence at Harvard University and the mastermind of the Data Map, first envisioned in 1997 and used to discover former Massachusetts governor William Weld's medical records in a redacted data set.
"Suppose you know someone went to the hospital," Sweeney said. You might know the name of the hospital, the data of admission, and maybe something about why they were there. "It's also the same kind of information that a financial institution would know about someone who said they were going to be late making credit card payments, because of a hospitalization," she said. "It's also the same kind of thing that a data mining company would know could extract from purchasing pharmacy data."
Another source of such data is news stories, so Sweeney and Robertson surveyed the NexisLexis online researcher service, and by tapping only three news sources in the state of Washington, the team was able to search for mentions of hospitalizations, and identified 81 subjects, many in news stories identified by their names, their ages and what happened to them.
Through some other searches on the public Internet, the investigation exactly identified 35 of the subjects, a 43 percent success rate. Sweeney then hired a temp who could use computers but didn't have a specific background in computer science, statistics, or medicine. The temp had two days to match the remaining 46 subjects using ordinary Internet searches, and was able to match every one of them.