Every marriage is many marriages. A relationship feels different when experienced in different life stages, or when viewed through the eyes of one partner or another. But what does it look like as a whole? How do you chart the rise and fall of conflict, contentedness, and shared activities that make up a life together?

To answer that question, sociologists Paul Amato from Pennsylvania State University and Spencer James of Brigham Young University examined data from 1,617 participants in the Marital Instability over the Life Course survey, a longitudinal study of marriage in the US conducted from 1980 to 2000. All respondents were married at the start of the survey; by the end, about half of them still were, the rest having divorced (19%), become widowed (5%), or dropped out of the study.

In a chapter of the recently published textbook Social Networks and the Life Course, Amato and James pulled out respondents whose partnerships ended in divorce and charted them separately from those whose marriages endured. Rather than focusing simply on marital “happiness”—a fuzzy and nebulous concept—they also looked at both the couples’ reports of discord and the number of activities they shared together.