Whether a wife is agreeable and in good health, however, doesn't play as big a role in predicting marital harmony, the researchers found.
"It's the husband's health more than the wife's that is associated with conflict in marriage," said James Iveniuk, lead study author and a Ph.D. candidate at the University of Chicago.
While previous studies have looked at the quality of a marriage or long-term partnership and its effect on health, Iveniuk and his team wanted to understand how the reverse direction might work. So, they looked at how health and personality characteristics affect late-life marital conflict.
For the study, Iveniuk used data from a national survey that analyzed 953 heterosexual couples, married or cohabitating. The men and women were aged 63 to 90 and their relationships, on average, had lasted 39 years.
The study was published recently in the Journal of Marriage and Family.
The researchers analyzed information about each partner's health and other characteristics, such as their tendency to be agreeable and a measure the authors describe as "positivity" -- how important it was for the partner to be viewed in a positive light.
Personality traits, such as extraversion, were also considered. Extraversion describes not only how outgoing a person is, Iveniuk said, but also how energized that person is by socializing, how impulsive and their degree of self-control.
To gauge marital conflict, the researchers took into account how much one partner tended to criticize the other, make too many demands or get on the other's nerves.
"If the husband's health is bad, the wife is more likely to report high levels of conflict," Iveniuk said.
But the opposite was not true. The husband's health may have a greater impact on the wife, Iveniuk noted, because wives are more likely to be asked to provide nurturing and caretaking. If the wife is ill, the husband may get another family member to step in and help, he suggested.
If the husband had high levels of positivity, there was also less conflict, Iveniuk found. The opposite was not true -- the amount of positivity the wives displayed had no effect on the husbands' reports of conflict.
However, if men were easily stressed out or were very extraverted, the wives tended to complain more about the marriage, Iveniuk found. The stressed-out person tends to be a difficult person to live with, he said, and wives may bear the brunt of that more than husbands with stressed-out wives.
Wives married to husbands who score high on extraversion may find it difficult to ''tame them,'' Iveniuk said, and find it hard to deal with their high energy level and impulsivity.
An expert who was not involved with the study said its findings may also reflect women's tendency to take things personally.
Traditionally, "women are far more responsive to the feelings of others, the behavior of others. We're reared to be more sensitive to how others relate to us," said Jamila Bookwala, a professor of psychology at Lafayette College, in Easton, Pa., who also studies marital quality.
If a husband is more positive, the wife is likely to feel her marriage is much better. "If she's a grouch, he is less affected by it," she said. Men may simply be better at shrugging off perceived slights and criticisms, she suggested.
Other research has found, in general, that older men rate marriage quality higher than do older women, Bookwala said.
Couples in long-term unions might take a step back and think about whether they could do things differently to preserve or increase harmony, Bookwala and Iveniuk agreed.
"Take a look at your reaction [to conflict]," Iveniuk said. If a man's inclination is to withdraw at the first sign of trouble and leave the discussion, maybe he could stay and talk it out.
Women might realize that they tend to be more relationship focused, and also be aware that this can actually make them more vulnerable to criticism, Bookwala said.
To learn more about keeping relationships healthy, visit the American Psychological Association.