A generation ago, the typical doctor owned a private practice, and saw patients whenever they got sick. Today, doctors are much likelier to work for large group practices or hospitals and be on call at predictable times. Seventy percent of doctors under 40 are now employees, not owners, according to American Medical Association data. So are the majority of female doctors of all ages.

Large group practices are more profitable because they can share resources, like clinic space or physician assistants, and more easily negotiate with health insurance plans.

But the setup also gives doctors more work-life balance, because there are more people who can serve as substitutes and divide night and weekend work.

“The old market expectation that your doctor will be available at all hours and is entirely flexible was beginning to fall apart as the work force became more diverse,” said Robert Wachter, chair of the department of medicine at the University of California, San Francisco. “New generations look at the work-life balance of older generations of physicians, and I think many of them say, ‘I don’t want that.’”

Dr. Wachter was responsible for naming one of the jobs that exemplifies this shift: hospitalist, the physician who sees patients who are hospitalized and coordinates with the specialists caring for them. They also make doctors’ schedules predictable, because hospitalists work in shifts, and primary care physicians don’t have to go to the hospital when their patients do. Other occupations have also come to rely on substitutes, like pharmacists and real estate agents (and in rare cases, some lawyers and management consultants).

Sara Gonzalez, 37, a pediatrician in Dartmouth, Mass., works as a hospitalist and in the emergency department, another shift job. She usually works 10 eight-hour shifts a month, with a few 16-hour overnights. When she’s off, she’s responsible for anything that comes up with her 1-year-old daughter; when she’s at the hospital, her wife, who works in marketing, is the on-call parent.