IGHE and Alzheimer disease: Finally, based on the bSRWPSO-FKNN and the medical dataset (AD), the key features affecting AD are extracted by 10 times 10-fold cross-validation experiments, mainly including the content of lymphocytes (LY), Cat dander, Milk, Dermatophagoides Pteronyssinus/Farinae, Ragweed, Cod, and Total IgE.