To further, test their ability to diagnose cognitive decline, a Receiver Operating Characteristic (ROC) curve (a graphical plot used to show the diagnostic ability of binary classifiers) method show that the abundance of Cl. phage vB CpeS CP51, Lc. phage jm3, Sc. phage 1717, St. phage P7132, and Lc. phage ul36 show an area under curve (AUC) of 0.54, 0.54, 0.58, and 0.56 to 0.58 (Fig. 2e), suggesting that these individual viral species have 54 to 58% confidence/ability to discriminate MCI from cognitively healthy controls. This evidence concerns the gene CYP51A1 and Mental deterioration.