Whenever I see references to research showing that married people live longer / are healthier / etc. than singles, I wind up wondering whether this is due to concomitant factors which exert on BOTH health AND the likelihood of marriage.
I hypothesize: People with certain maladaptive traits will act in ways that increase their health risks. These same traits make them undesirable as spouses. Hence the presence of these people in the singles sample, who put themselves at risk more often and die earlier, skews the sample and makes it APPEAR as though marriage increases longevity.
Does the existing research control for this?