Researchers at the University of Pennsylvania found that patients who are divorced, separated, or widowed had approximately a 40% greater chance of dying or developing a new functional disability in the first two years following cardiac surgery than their married peers. The data included 1576 subjects who underwent cardiac surgery, of which 65% were married; 33% were divorced, separated, or widowed; and 2% had never been married. The findings were reported to be statistically significant. Marc Neuman and Rachel Werner, "Marital status and postoperative functional recovery," Journal of the American Medical Association Surgery, 151 (2016), pp. 194- 196. Some variables might differ between the subjects in the study who were married versus those who are divorced, separated, or widowed. @ Macmillan Learning Identify if any of these variables are possible confounding variables. price of the surgery access to care length of the surgery financial support emotional support