Delirium is an important postoperative complication, yet predictive risk factors for postoperative delirium severity remain elusive. We hypothesized that the NSQIP risk calculation for serious complications (NSQIP‐SC) or risk of death (NSQIP‐D), and cognitive tests of executive function (Trail Making Test A and B [TMTA, TMTB]), would be predictive of postoperative delirium severity. Further, we demonstrate how advanced statistical techniques can be used to identify candidate predictors.. To read the full article, log in using your NHS Athens details. To access full-text: click “Log in/Register” (top right hand side). Click ‘Institutional Login’ then select 'OpenAthens Federation', then ‘NHS England’. Enter your Athens details to view the article.