In July, Jennifer O’Brien got the phone call that adult children dread. Her 84-year-old father, who insisted on living alone in rural New Mexico, had broken his hip. The neighbor who found him on the floor after a fall had called an ambulance.

Ms. O’Brien is a health care administrator and consultant in Little Rock, Ark., and the widow of a palliative care doctor; she knew more than family members typically do about what lay ahead.

James O’Brien, a retired entrepreneur, was in poor health, with heart failure and advanced lung disease after decades of smoking. Because of a spinal injury, he needed a walker. He was so short of breath that, except for quick breaks during meals, he relied on a biPAP, a ventilator that required a tightfitting face mask.

He had standing do-not-resuscitate and do-not-intubate orders, Ms. O’Brien said. They had discussed his strong belief that “if his heart stopped, he would take that to mean that it was his time.”

Listening in on the phone while a hospital palliative care nurse-practitioner talked to her father about his options, Ms. O’Brien provided a blunt translation to an always blunt man: “Dad, your heart and lungs are done.”

The next day, he declined surgery to repair his hip. A startled anesthesiologist and an orthopedist called his daughter, apparently expecting her to talk her father into agreeing to the operation. She didn’t try.

“He was dying,” she said in an interview. “He’d either die comfortably or, with a big surgical incision, he’d die uncomfortably. Or die of something more complicated — potential infections, bowel obstructions, so many things that can happen.” Mortality rates after hip fractures, though improving, remain high.

Her father, who wasn’t cognitively impaired, had decided that surgery was “silly” and unnecessary. She supported his decision and contacted a local hospice.

Families often have to run interference in such scenarios, and a new study in JAMA Network Open helps explain why. The authors, most of them at Case Western Reserve University School of Medicine, analyzed five years of data from a cancer registry, nursing home assessments and Medicare claims to look at “aggressive end-of-life care” among 146,000 older patients with metastatic cancer.

They compared nursing home residents’ care in the last 30 days of their lives with the care for non-institutionalized patients living in communities, the lead author, Siran Koroukian, a health services researcher at Case Western Reserve, said.

The team looked for commonly used markers of aggressive care, including cancer treatment, repeated emergency room visits or hospitalizations, admission to an intensive care unit, lack of hospice enrollment until three days before death, and death in a hospital.

“In all probability, hospice should have been considered” for these patients, said Sara Douglas, a co-author and oncology researcher at the Case Western Reserve University School of Nursing.

Yet the majority of both groups — 58 percent of community dwellers and 64 percent of nursing home residents — received aggressive treatment in their final 30 days. A quarter underwent cancer treatment: surgery, radiation, chemotherapy.

Although studies repeatedly show that most patients want to die at home, 25 percent of the community dwellers and almost 40 percent of the nursing home residents died in hospitals.

Hospice leaders, palliative care specialists, health care reformers and advocacy groups have worked for years to try to lower such numbers. “Patients who received this type of aggressive care experience more pain, actually die sooner, have a much poorer quality of life at the end. And their families experience more doubt and trauma,” Dr. Douglas said.

Because the researchers used large databases, the study can’t indicate whether some patients actually opted for continued treatment or hospitalization. Some treatments the authors deemed aggressive could instead have been palliative, intended to increase comfort, like radiation to shrink tumors that might impede breathing.

Still, “these are really sobering statistics,” said Douglas White, director of the Center for Ethics and Decision Making in Critical Illness at the University of Pittsburgh School of Medicine.

A lot of factors contribute to invasive actions in patients’ final days and weeks. Some originate within the health care system itself. Doctors may be reluctant to initiate difficult conversations about what dying patients want, or be poorly trained in conducting them.

“The minute you have this conversation, people assume, ‘You’re giving up on me,’” Dr. Douglas said. Even having an advance directive and a Physician Order for Life-Sustaining Treatment, or P.O.L.S.T., doesn’t always ward off aggressive treatment.

But studies also show that even when crucial discussions take place, patients and surrogate decision-makers frequently misinterpret them. “Families often leave these conversations with much more optimistic expectations than their doctors meant to convey,” Dr. White said.

His research has documented the effects of optimism bias. Surrogates understand positive prognoses more accurately than negative ones. They may grasp that most people in this situation will die, but insist that their particular loved one is different, fiercer, stronger. Misplaced optimism then leads to more aggressive treatment.

Sometimes, family demands prevail even over the patient’s own wishes. Jennifer Ballentine, chief executive of the Coalition for Compassionate Care of California, knew that one of her relatives didn’t want high-intensity care if he became terminally ill. But when he developed aggressive prostate cancer at 79, his wife insisted that he pursue treatment.

“He refused. He kept saying he just wanted to be in hospice,” Ms. Ballentine recalled. “She kept saying, ‘Absolutely not.’ ” He capitulated until, after three exhausting months of chemotherapy with several hospital stays, he died in hospice care.

The health care system could improve end-of-life care. When palliative care is introduced soon after a diagnosis, patients have a better quality of life and less depression, a study of people with metastatic lung cancer found. Though they were less likely to undergo aggressive treatment, they survived longer.

Palliative care doctors, skilled in discussions of serious illness, are scarce in some parts of the country, however, and in outpatient practices.

Adopting a so-called concurrent care approach to hospice might also ease these transitions. The Medicare hospice benefit requires patients to forgo treatment for their terminal illness; hospice through the Veterans Health Administration system, with more liberal criteria, allows patients to receive both treatment and hospice.

A recent study of veterans with end-stage kidney disease, who were likely to die within days if forced to discontinue dialysis, shows the impact of concurrent care. Palliative dialysis — administered less often or for shorter periods than the standard regimen — can help control symptoms like shortness of breath.

“Being required to stop a treatment that is helping your quality of life can mean that you won’t sign up for hospice,” said the lead author, Melissa Wachterman, a palliative care doctor at Harvard Medical School.

In her study, veterans who discontinued dialysis when they enrolled in hospice received just four days of care before they died, so short a time that even expert hospices would struggle to provide full support. Those receiving concurrent dialysis as hospice patients, almost all through the V.A., averaged 43 days of hospice care.

Medicare has authorized pilot studies of concurrent care, but for now, patients and families must often seize the reins to make their end-of-life wishes known and determine how best to fulfill them.

Some patients want every possible action taken to extend their lives, even briefly. For those who feel otherwise (former President Jimmy Carter, for instance), asking about palliative care and hospice can open the door to straightforward discussions.

James O’Brien was among the latter. His daughter drove 12 hours, from Little Rock to Santa Fe, to spend a quiet day with him. “We had some good time together,” she said. “We talked about what was going to happen.”

She was there as the hospice team provided medication to keep him comfortable and withdrew the biPAP. “It was very peaceful,” she said. “I told him I loved him. I knew he could hear me. I stayed with him until he took his last breath.”