Risk factors included by the risk stratification instruments for postoperative delirium.

<p>Abbreviation: APACHE, Acute Physiology and Chronic Health Evaluation.</p>a<p>The definition of some risk factors differed from their definition in the original studies (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0113946#pone.0113946.s001" target="_blank">Table S1</a>).</p>b<p>For some variables, N<292 due to missing data.</p>c<p>Letter fluency was measured in a subset of patients.</p><p>Risk factors included by the risk stratification instruments for postoperative delirium.