We then fit two regression models to explore the main and interactive effects of age and APOE status on total hippocampal volume (Table 2). In our first model examining the main effects in the absence of interactions between age and APOE, we observed a robust negative and non‐linear relationship between total hippocampal volume and age. Specifically, participants in the 60 to 69 age group had a 116.1 mm3 reduction in hippocampal volume compared to those younger than 60 (P = 7.4 × 10−61), and this effect magnified > 3‐fold in individuals aged ≥ 70 (β = −407.0 mm3, P < 10−300).
