NEW DELHI — When Elizabeth Brenner's 21-year-old son died while hiking during a study-abroad trip in India, she began searching for other cases and found only partial data and anecdotal records.

"Nobody was keeping track of this at all," she said.

Brenner's son, Thomas Plotkin, was one of the millions of American students who have studied abroad in the last decade — part of a growing global youth travel industry estimated to be worth $183 billion a year.

The number of American students studying abroad has doubled in the last decade. But while U.S. colleges and universities must report deaths on their campuses, they are not required to disclose most student deaths that occur abroad and the U.S. Department of Education keeps no such statistics.

A group called the Forum on Education Abroad pulled together information for 2014 from two insurance companies that together cover half of the U.S. study-abroad market. The group used the partial data to conclude in a 2016 report that students are less likely to die overseas than on a U.S. campus.

Brenner and other parents slammed the report, saying the findings are misleading and give parents the idea that programs are safer than they may actually be.

The forum is now planning to release a new report later this year with information for 2010-15, but it will still cover only half of the market. The forum's head, Brian Whalen, said they tried to get the exact number of student deaths overseas from the U.S. State Department, but were told it wasn't available.

Ros Thackurdeen, whose son Ravi drowned on a school-sponsored excursion to a beach in Costa Rica in 2012, has since amassed news reports and travel alerts documenting 3,200 students who died or were kidnapped, drugged or injured abroad in recent decades. For 2014, she counted 14 student deaths — far higher than the four listed by the forum that year.

"Coffee beans and bowling balls have more rules than any program, school, professor or teacher escorting our kids into foreign countries," said Sheryl Hill, who built a business called DepartSmart around providing safety advice to traveling students, after her 16-year-old son, Tyler, fell ill and died while studying in Japan in 2007. She said he had Type 1 diabetes and died from dehydration when he did not receive medical attention in time.

Grieving parents successfully lobbied for legislation in Minnesota in 2014 and in Virginia two years later to regulate the study-abroad industry. A similar measure has been introduced in New York, and one member of Congress is now pushing a nationwide bill.

"Knowing which areas are hotspots for violent crime is important information for kids and parents to know when they're making decisions on where they'll study abroad," said Rep. Sean Maloney, a Democrat from New York who introduced the Ravi Thackurdeen Safe Study Abroad Act in Congress in 2014 and plans to reintroduce it in September.

Gregory Malveaux, study-abroad coordinator at Montgomery College in Maryland, published a 2016 book on study-abroad safety. He backs the idea of mandating institutions to release data on student deaths and injuries.

"If this data exists on-campuses, it needs to also cover off-campuses," Malveaux said.

The lure of studying abroad is strong, and universities are offering more programs than ever.

Federal legislation introduced last year aims to boost the annual number of Americans studying abroad to 1 million by providing more grants and incentives.

"Far too few executives have the skills to be truly successful in unfamiliar cultural waters," said Downing Thomas, the dean of international programs at the University of Iowa, which sends more students to India than any other U.S. institution.

There are other benefits as well.

"It contributes to personal growth through greater independence, deeper self-knowledge and greater tolerance for ambiguity," said Brad Farnsworth, vice president of the American Council on Education.

But many American universities and colleges are unable to finance or manage such programs, and instead refer students to independent, third-party operators.

These independent operators are not authorized to give college credits. So they partner with accredited institutions, often different from where the student is enrolled.

Thackurdeen said the setup was duplicitous. "These universities offer these programs as if it's theirs," she said from her home in Newburgh, New York.

Her youngest son had been studying at Swarthmore College in Pennsylvania, but his tropical medicine course in Costa Rica was being accredited through Duke University. After Ravi died, Swarthmore stopped backing that program offered by the Organization of Tropical Studies.

When Plotkin died on his 2011 trip to the Indian Himalayas, the University of Iowa, where he had been enrolled, cut ties with the organization that ran the course, the National Outdoor Leadership School.

Earlier this year, Plotkin's mother spent two months on a "pilgrimage" tracing a winding, 1,037-mile trail along the Goriganga and Ganges rivers to where the water empties into the Bay of Bengal.

Brenner believes this is the path her 21-year-old son's body traveled after he fell from a mountain trail and disappeared into the water, never to be seen again.

"I still feel a tremendous amount of grief," said Brenner, from Minnetonka, Minnesota. "I'll have to figure out how to carry that for the rest of my life."