APOE and Alzheimer disease: When examining the stratum-specific RR for the APOE ε4 allele type, only the risk reduction for the occurrence of AD (0.74 [0.55–0.99], p = 0.036), but not that for MCI, reached statistical significance for C + participants carrying the APOE ε4 allele compared with C- participants (Table 3, + APOE ε4, column 2).