# Modeling APOE, morbidity, and mortality: a reproducibility challenge for genetic epidemiology

## TL;DR

This paper discusses how inconsistent results in APOE research on aging and mortality are often due to differences in study design and analysis choices, not biological complexity.

## Contribution

The paper introduces new conceptual principles to improve reproducibility in APOE studies by addressing modeling choices and reporting practices.

## Key findings

- Inconsistent APOE findings are largely due to analytical decisions, not biological complexity.
- Selective exclusion of rare genotypes and overadjustment contribute to irreproducibility.
- Standardized baseline models and inclusion of all observed genotypes are recommended for better reproducibility.

## Abstract

APOE is among the most extensively studied genetic loci in research on aging, morbidity, and mortality. Despite its well-established biological roles, empirical findings on the association between APOE and mortality remain inconsistent across studies. This heterogeneity is often attributed to biological complexity. In this Perspective, we argue that much of the apparent inconsistency instead reflects differences in modeling choices, variable definitions, and reporting practices, resulting in limited reproducibility and comparability. We highlight how pleiotropy, age-dependent effects, and selective survival make APOE particularly sensitive to analytical decisions. We focus on three underappreciated sources of irreproducibility: selective exclusion of rare APOE genotypes, lack of standardized baseline models, and routine adjustment for variables that are not confounders under Mendelian inheritance. We argue that all observed APOE genotypes should be included in primary analyses, that parsimonious baseline models adjusted only for variables independent of genotype should always be reported, and that overadjustment can obscure rather than clarify genetic effects. We propose a set of conceptual principles to improve reproducibility in studies of APOE, morbidity, and mortality, with implications for genetic epidemiology more broadly.