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The divorce rate in the U.S. has been on a steady decline. New data reveal that the 2015 divorce rate dropped to the lowest overall rate in 40 years, according to the National Center for Family & Marriage Research at Bowling Green State University in Bowling Green, Ohio.

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While no one knows what makes individual couples fight for their marriage and others to just give up, perhaps a fair number of happily married couples know how to "map" -- or keep details about their spouse stored in their mind.

Dr. John Gottman, professor of psychology at the University of Washington in Seattle, has learned that the secret to love is in the details.

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Gottman presented key findings from over 30 years of research in his best-selling book, "The Seven Principles for Making Marriage Work." Many of his conclusions come from direct observation of married couples in his "love lab" -- a set of apartments in which Gottman and his research team observed volunteer couples through one-way windows and video cameras.

Gottman studied newlyweds and found that 67 percent of couples saw a significant drop in marital satisfaction after becoming first-time parents. The other 33 percent remained at least as happy as they were before, but half of these experienced increased martial satisfaction.

The secret ingredient in the marriages of couples who thrived after becoming first-time parents is that they had what Gottman called detailed "love maps." In his book, Gottman described a love map as the part of the brain in which spouses store all the relevant information they have gathered about each other. Relevant information includes things like details about their history, food preferences, hobbies, and sports interests.

Couples don't start their relationships with love maps; they have to create them over time. Married couples who do this -- and update the information as their spouse's world changes -- set themselves up for a happy, lasting marriage.

My wife and I have been building our love maps for almost three decades. Here are my best tips for spouses who want to start creating theirs, or build on the information they have already.

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Jon Beaty, life coach and father of two, lives near Portland, Oregon. He’s the author of the book “If You’re Not Growing, You’re Dying: 7 Habits for Thriving in Your Faith, Relationships and Work.”