Co-authors Geoffrey Greif, DSW, MSW, professor at the University of Maryland School of Social Work, and Kathleen Holtz Deal, PhD, MSW, associate professor at the School, have found that when couples agree on how they spend their time alone and with others, they are more likely to have a happy marriage or relationship.
The book, "Two Plus Two: Couples and Their Couple Friendships," offers language that couples can use to talk with each other to find a balance that works for them.
The findings are based on interviews with 123 couples with both partners present, 122 individuals who were alone when questioned about their relationships, and 58 divorced individuals.
To identify and interview subjects for the study, the professors began with the work of 58 master's students in an advanced research course and then interviewed more than 20 couples themselves.
The research found differing motivations behind couples' friendships, with some people preferring to share emotions while others see the purpose as fun and recreation.
The ways the friendships get started also vary, with the majority growing out of a typical friendship between two people that widens to encompass all four.
Deal, who has been married 43 years, said that she was surprised to find that she and her husband were in the minority because they set out as a pair to make friends with other couples.
They established friendships with a group of five other couples that have lasted for over 30 years. They have shared social events and vacations.
"We can talk about anything we want to. We have shared sad times, and good times," she said, calling the group of friends, who met one another at church, "a huge influence on my life."
Greif said that he and his wife of 36 years "feel very comfortable" in their friendships with other couples and that work on the book has given him the "language to think about how couple friendships are begun and how they are maintained."
Greif and Deal concluded that healthy couple friendships increased partners' attraction to each other, provided a greater understanding of men and women in general, and allowed partners to observe ways that other couples interact with each other and negotiate differences.