A federal shield law would protect reporters and their anonymous sources unless prosecutors could show a need, by a preponderance of evidence, that revealing the sources would prevent imminent harm to national security or imminent death or significant physical injury. The 2007 version of the Free Flow of Information Act also would not have protected sources if they disclosed trade secrets, health information or nonpublic personal information that violated a law.

A total of 49 states have shield laws or operate under court rulings that grant journalists and their sources a privilege like those afforded to lawyers and therapists and their clients.

The study, which Jones began at the University of Arizona, helps quantify the problem for judges and legislators, said Gregg Leslie, legal defense director for the Reporters Committee for the Freedom of the Press. Judges often struggle to understand why subpoenas are a burden for newsgathering, and Congressmen and women have balked at considering the issue without knowing how widespread it is.

"It's a staggering achievement to get a lot of data together like this," Leslie said. "We certainly are indebted to her."

Jones said the neutral data should move the dialogue past subpoena frequency to more substantive issues.

"I hope now they can move past dialogue on subpoena frequency to more substantive discussion on whether a shield law is a good idea," she said. "It's time to move past whether subpoenas are really being issued, because they quite clearly are."

Jones herself was subpoenaed for information about a story she wrote for the Salt Lake Tribune about a criminal trial in the mid-1990s. She wasn't compelled to testify, but she recalled feeling shaken.

Jones later served as a law clerk for U.S. Supreme Court Justice Sandra Day O'Connor in 2003-04. She is now working on a follow-up article with other data from the BYU survey about the real impact of subpoenas on newsgathering.

"Newsroom leaders chimed in on what they thought the impact of the subpoenas was, in terms of money and time and interruption of the process," she said.

E-mail: twalch@desnews.com