Investigative journalist David Donald in 2015 at the Shard observation deck in London. (Family Photo)

David Donald, an investigative journalist who was long at the frontier of computer-assisted reporting and whose command of large data sets helped propel stories about the underreporting of sex assaults on college campuses, the 2008 financial crisis and bill-padding among Medicare providers, died Dec. 10 at a hospital in Reston, Va. He was 64.

The cause was complications from mesothelioma, a form of cancer, said his wife, Joyce Donald.

Since 2014, Mr. Donald had been affiliated with American University’s Investigative Reporting Workshop. He previously was data editor at the Center for Public Integrity, a nonprofit investigative journalism group in Washington, and training director at the Missouri-based Investigative Reporters and Editors (IRE) organization.

Mr. Donald was variously a high school English teacher, a bard (with a focus on verse about the natural world) and an outdoor-equipment salesman, all in his native Ohio, before switching to journalism in his late 30s. Computer-assisted data analysis was becoming more common in newsrooms, and in time Mr. Donald plunged into high-profile reporting projects that involved terabytes of information.

His most notable work was conducted at the Center for Public Integrity, where he was on staff from 2008 to 2014. With painstaking effort, he wrestled with colossal amounts of data and applied the analysis techniques of social-science researchers. “We borrow — in reality, we steal — their methods,” Mr. Donald once quipped.

The project “Cracking the Codes” (2012) documented the abuse of the government-run Medicare system by thousands of doctors, hospitals and other medical providers who billed for costly, often unneeded treatments for seniors, sometimes after not performing the medical service at all. The story, which ran in The Washington Post, said that such “upcoding” amounted to $11 billion in fraudulent fees over the previous decade.

The 21-month investigation received the Philip Meyer Award, one of journalism’s highest honors for data-driven reporting, and compelled the Justice Department and the Department of Health and Human Services to promise heightened scrutiny of and the threat of prosecution for Medicare-related corruption.

Mr. Donald was also immersed in the Center for Public Integrity’s joint 2009 investigation with NPR called “Sexual Assault on Campus.”

When he saw the relevant data collected by the Education Department, “it was unreal because you had large campuses . . . that had 40, 50, 60,000 students and no rapes or sexual assault,” Mr. Donald said in an IRE video. “You put together a bunch of young folks and everything, it just didn’t make sense.”

His team distributed surveys not to college presidents but to those who knew the topic best: workers at health clinics on and near campuses. “Lo and behold,” he said, “on many universities that claimed zero or one rape, the health clinics were reporting dozens every year.”

Using Education Department data, the reporters also uncovered how the universities adjudicated sex assaults — often through secretive disciplinary proceedings and other practices that effectively silenced the victims. The federal government, Mr. Donald said, often gave colleges “a slap on the wrist” for mishandling or failing to report campus rapes.

The story received the Sigma Delta Chi Award for public service in online journalism, and the NPR report earned a Peabody Award, a top broadcasting honor. Soon after the reporting, Vice President Biden announced new guidelines for schools to prevent and respond to campus sexual assaults.

“Like good social scientists,” Mr. Donald said in the IRE video, “we made the data available to other news organizations, and a lot of them localized it to fit their universities or their regional area, so it had impact that way as well.”

John Dunbar, now the Center for Public Integrity’s chief executive, worked as a reporter with Mr. Donald on “Who’s Behind the Financial Meltdown?” (2009), which identified the largest subprime home mortgage lenders. Defaults on those mortgages were thought to be a leading factor in the financial collapse.

The data collected by Mr. Donald spurred further reporting by the center into how Wall Street megabanks backing the mortgage lenders were being bailed out by the government — in essence, how they were rewarded for destroying the economy.

“It’s hard to argue with hard data,” Dunbar said. “You can twist it around however you want, but when it’s presented by someone who knows that they’re doing, it’s very compelling evidence.”

David Charles Donald was born in Cincinnati on June 5, 1952, and he grew up in the Cleveland suburb of Berea. He was a 1974 graduate of Miami University in Ohio and in 1980 received a master’s degree in English from Cleveland State University; his thesis was a volume of original poems.

He spent much of the next decade in sales, turning to journalism because of what he called his “need to go back to my world of words.”

He received a master’s degree in journalism from Ohio’s Kent State University in 1997, a degree he completed while working in computer-assisted journalism at the Savannah Morning News in Georgia.

Survivors include his wife of 34 years, Joyce Winkle Donald of Reston; a son, Ryan Donald of Lithonia, Ga.; and two brothers.

During those years in Savannah, Joyce Donald said of her husband, “He taught himself SQL and other computer languages, and he’d still read me poetry at night when we were together.”