[dj_mc_merlin]

That is not correct, the article talks about methodology:

> The patients were all Medicare beneficiaries aged 65 to 99. They had all undergone one of 17 common emergency surgical procedures between 2011 and 2014. Examples of those 17 procedures included cardiovascular surgeries, hip and femur fracture, appendectomy, and small bowel resection. The study focused on emergency surgery, so as to minimize the potential selection bias. For example, surgeons might otherwise choose patients based on their illness severity, or patients might choose their surgeon.