For years now, we've been hearing that workers want flexibility in their schedules. It's one of the biggest reasons so many people are jumping on the freelance bandwagon. But according to a new study from the University of California-Berkeley and the University of California-San Francisco, schedules that constantly shift might be a real killjoy.

Less notice, blacker mood

For the study, researchers looked at survey data from about 28,000 workers from 80 American retail firms. The survey sought to figure out how scheduling practices affected the employees.

When workers had more than two weeks' notice of their schedule, the likelihood they'd be happy was about 75 percent. When notice was significantly shorter (two days), the likelihood of happiness dropped a full 10 points to 65 percent. Additionally, a quarter of retail workers said their companies practiced on-call scheduling, meaning the workers didn't have a guarantee they'd work or get paid for a particular shift. On call workers were 9.2 percent less likely to report feeling happy.

Why the happiness slump?

Alix Gould-Werth, senior policy analyst with the Washington Center for Equitable Growth, offers a simple explanation for why predictability in scheduling makes such a difference in happiness: While work hours certainly aren't the only thing that influences your joy, scheduling still affects many parts of your life, such as being able to make appointments or spend time with friends. If you don't have that predictability, it's much more difficult to plan the rest of what you want to do. That can raise stress and conflict with others, and there's a higher risk that, if you do make plans, you'll end up disappointed.

In other words, it's not really the schedule itself that's the problem. It's the lack of personal control. When workers have to just roll with whatever an employer needs, it interferes with their larger sense of autonomy. Nobody likes to feel like a puppet, and when people don't know what's upcoming, it's much harder to figure out what self-protective measures they need to take.

Gould-Werth suggests that companies turn to less predictable scheduling as a way to reduce their own risks--it allows them to adapt quickly to immediate customer demands. But as a leader or boss, it's worth remembering that happiness can boost productivity. That's in part because we're not as distracted by stress. But it's also because being happy affects how we interact with others. The happier we are, the more socially attractive we can seem to others, and the greater the likelihood of strong collaboration subsequently is.

While there's a risk in being less responsive to the demand you see in the market, there's risk from low worker morale and cohesion, too. Because the stresses individual teams have aren't identical, it's up to you to communicate well with your employees about how much notice they need to avoid a crash in mood. Don't assume you can just make it up to them in wages, because according to the study, more cash actually had less of an influence on happiness than if workers were able to avoid a shift cancellation.

Money, we're once again reminded, isn't everything.