A Note on The Rationale Behind Using Parental Longevity as a Proxy in Mendelian Randomization Studies

TL;DR

This paper clarifies the assumptions and causal reasoning behind using parental longevity as a proxy for participant longevity in Mendelian Randomization studies, addressing a common but under-explained practice.

Contribution

It explicitly states the assumptions and causal effects enabling the use of parental lifespan as a proxy in MR studies, filling a gap in the literature.

Findings

Clarification of assumptions behind proxy use

Explanation of causal effects involved

Guidance for future MR studies using proxies

Abstract

In many cohorts (such as the UK Biobank) on which Mendelian Randomization studies are routinely performed, data on participants' longevity is inadequate as the majority of participants are still living. To nevertheless estimate effects on longevity, it is increasingly common for researchers to substitute participants' `parental attained age', i.e. parental lifespan or current age (which is routinely collected in UK Biobank), as a proxy outcome. The common approach to performing this clever trick appears to be based on a solid understanding of its underlying assumptions. However, we have not seen these assumptions (or the causal effects whose identification they enable) clearly stated anywhere in the literature. In this note, we fill that gap.