Associate sociology professor Julie Brines, PhD, and doctoral candidate Brian Serafini didn’t set out to look for seasonality in divorce rates; they initially wanted to study the effects of the recession on marital stability. But when they began analyzing divorce filings in Washington State between 2001 and 2015, they were surprised to see a consistent pattern emerge.

“It was very robust from year to year, and very robust across counties,” Brines said in a press release. The spikes remained even after they accounted for things like unemployment and the housing market, which also tend to follow seasonal patterns.

The researchers speculate that couples avoid filing for divorce around Christmas and New Year’s, as well as when school is out for the summer, because these times are considered sacred to families. “Family life is governed by a ‘social clock,'” they write, “that mandates the observation of birthdays, holidays, or other special transitions involving family members over the course of a year.”

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Filing for divorce during these special periods may be socially unacceptable to many couples, they say. And some unhappy husbands and wives may even think that spending a happy holiday or a nice family vacation together will help heal their troubled marriages.

“People tend to face the holidays with rising expectations, despite what disappointments they might have had in years past,” Brines said. “They represent periods in the year when there’s the anticipation or the opportunity for a new beginning, a new start, something different, a transition into a new period of life.”

Unfortunately, she adds, holidays often don’t live up to those expectations. In fact, they can be so stressful and emotionally charged that, for some failing marriages, they may be the last straw—what she and other sociologists refer to as a “broken promises” scenario.

Brines suspects that couples need a few months to secure lawyers, get finances in order, and to work up the courage to file for divorce, hence the gap between New Year’s and the first noted spike in March. The same logic may apply in the summer after a month or two of family leisure time, she says, although the start of the school year could speed up the timing for couples with children and account for the second spike in August.

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She also notes that suicides tend to peak in the spring, as well, and that some experts say that longer days and increased activity can elevate mood in people with depression enough for them to act on their suicidal thoughts. It’s possible, she says, that similar factors could motivate fed up couples to take action, too.

The researchers presented their research as a working paper this weekend at the annual meeting of the American Sociological Association, and are now studying other states to see if their findings hold true in a larger sample size. So far, they’ve looked at Ohio, Minnesota, Florida, and Arizona. And despite differences in demographics and economic conditions in those states, they say, the seasonal divorce pattern “is more or less the same.”

This article originally appeared on Health.com