There is a common perception that as people spend more time together, they begin to act and think more alike. They may even look more alike.  This synchrony, or interdependence, between a couple posits that a married person's cognitive functioning or health influences not only their own well-being but also the well-being of their partner.

A new paper finds that this interdependence continues even when one of the partners passes away and his or her characteristics continue to be linked with the surviving spouse's well-being. 

Lead author Kyle Bourassa, a psychology doctoral student at the University of Arizona, and colleagues turned to the multinational, representative Study of Health, Ageing, and Retirement in Europe (SHARE), an ongoing research project with over 80,000 aging adult participants across 18 European countries and Israel. Specifically, they examined data from 546 couples in which one partner had died during the study period and data from 2566 couples in which both partners were still living.

As expected, the researchers found that participants' quality of life earlier in the study predicted their quality of life later. And the data also provided evidence for interdependence between partners - a participant's quality of life earlier in the study was associated with his or her partner's quality of life later. But interdependence between partners remained even when one partner died during the study; they believe they controlled for other factors that might have played a role, such as participants' health, age, and years married.

There was no observable difference in the strength of the interdependence in couples' quality of life when comparing widowed spouses with spouses whose partners remained alive. Importantly, the results from first group of couples were replicated in a second, independent sample of couples from the SHARE study, bolstering the researchers' confidence in the findings.

Although the study does not address the mechanisms underlying interdependence between partners, Bourassa and colleagues hypothesize that ongoing interactions are a likely driver of synchrony in intact couples, while the thoughts and emotions generated by reminiscing may explain interdependence for those who lost spouses.