SACRAMENTO, Calif. — At the statistical intersection where increased life expectancy balances out the divorce rate, there is a surprising new cultural demographic: More Americans are reaching and exceeding the 40th wedding anniversary.

What’s keeping more married couples together till death do them part? Todd Migliaccio, a Sacramento State associate professor of sociology, is working to figure that out in a series of interviews with couples married 30 years or longer, or with a surviving spouse.

“We tend to focus on the fact that more people get divorced now,” said Migliaccio, 37. “But maybe we should focus on the increasing number who stay married longer.”

It’s a sunnier approach, after all. There’s only so much the group most at risk of divorce — newlyweds married five years or less — have to share with the world. On the other hand, couples who have stuck it out through thick and thin might have a few things to teach us.

So far, Migliaccio has interviewed six couples. His plan was to videotape them talking about their long and happy marriages as a way to sweeten the dose of reality he provides students in class.

“I have students who, at the end of class tell me, ‘I don’t want to be married,’” he said. “I tell them, ‘This is not about scaring you. It’s so you can go into marriage with open eyes.’”

Compare that with the pop-culture focus on brides, wedding dresses and ridiculously expensive weddings, which all but ignores the fact that after the wedding comes the marriage.

“I knew I was in love when he went away on vacation with his parents,” said Barbara Metzinger, 79, who was married to her husband, Ernest, for 60 years when he died in 2007 at age 80. “While he was away on vacation, we both just about died being separated,” she said. “It was probably puppy love, but to us it was real. And it grew into a great big love.”

Judie Panneton and her husband, John, have been married almost 29 years. “If you weather storms together, which we have over the years, and if you grow closer rather than apart, then in the future you can weather just about anything,” said Panneton, 56.

OK, but what exactly does that involve?

Metzinger suggests negotiation, as well as having both shared and individual interests. Panneton says respect is the key.

They’re both right, says Migliaccio. Communication, respect and shared interests are among the themes emerging from his interviews.