The question is always: does the study show causality? "The people who were the most satisfied in their relationships at age 50 were the healthiest at age 80".

The question is always: does the study show causality? "The people who were the most satisfied in their relationships at age 50 were the healthiest at age 80". Can we think of ways that, for example, health problems at ages 45-50 cause (a) dissatisfaction in relationships at age 50 and (b) worse health problems at age 80? Did they control for that? (Is it possible to control for that? Even if they have their full clinical history, is it possible that problems that, at age 50, were subclinical—or "not reported to the doctor"—would have significant effects?)