For people who work in the service sector, unpredictable, unstable schedules have a range of negative consequences, including psychological stress and poor health, according to a new working paper from the University of Pennsylvania and the University of California, Berkeley.

“People have long-suspected that this was the case,” said Kristen Harknett, an adjunct associate professor in Penn’s Sociology Department in the School of Arts & Sciences. But “we haven’t had systematic evidence.”

Until now.

Harknett and colleague Daniel Schneider from Berkeley decided to focus on how two dimensions, amount of notice employees have for their work schedules and amount of instability in those schedules, affect the mental and physical health of workers. Because no existing datasets contained the information needed to address this topic, the researchers created their own.

They turned to Facebook, building ads targeted at 18- to 50-year-olds who were employed by eight of the largest retailers across the country, places where these scheduling practices commonly occur. The advertisement offered a lottery incentive to employees who took a 20-minute online survey. Harknett and Schneider have so far received about 6,000 responses.

Those given more lead time about work days and hours reported less stress, better overall health and less trouble sleeping, according to the sociologists, who surmise that such negativity can trickle down to children. In fact, they found that having more lead time also led to more time with children for working parents.

“There are a whole bunch of common sense reasons to care about this,” Harknett said.

Lawmakers have started to take notice of this connection between such practices and health and well being, with cities across the country putting worker scheduling laws to a vote. San Francisco became the first, in 2014, to pass such legislation, and in mid-September of this year, Seattle took similar steps. That city’s new law, which will likely take effect in July 2017, forces retailers and food establishments of a certain size to provide two weeks advanced notice of schedules, among other requirements. Harknett said that San Jose, Washington, D.C., and New York City are also considering these types of laws.

“There’s a lot of anecdotal evidence about how harmful these practices are and how difficult the lives of working parents are when they have a complete inability to plan,” she said. “If you don’t know your work schedule in advance, you can’t have a second job, you can’t go to school, you can’t have a regular child-care arrangement. Everything has to be arranged at the last minute.”

Part of how we got here has to do with technology, according to Harknett, who said she believes automated scheduling software benefited companies but failed to take into account the humans filling those spots. That problem reached an extreme and now, a tipping point.

Once more places have enacted laws that, for instance, require employers to offer added hours to existing part-time workers before they seek out new ones, what’s called “access to hours,” Harknett and Schneider plan to conduct before-and-after comparisons, looking at the period leading up to the law and the period following implementation.

“We’re hoping to take advantage of some of the differences, to get a sense of which of these factors matters most,” Harknett said.

They would also like to look further into family dynamics and the effect of a parent’s work schedule on the household’s children.

“This is a low-wage sector,” she said. “Higher-income families have more resources to deal with a volatile income, with a volatile schedule. When your resources are more scarce, it compounds the problem.”

Funding for the research came from the Washington Center for Equitable Growth and, at UC Berkeley, the Institute for Research on Labor and Employment, Hellman Fellows Fund and School of Public Health.