Disparate Effect Of Missing Mediators On Transportability of Causal Effects

Vishwali Mhasawade, Rumi Chunara

Keywords: Transportability, Mediation, Missing data

Abstract:

The transport of mediation effects is an important question for upstream interventions, such
as targeted development of parks to improve population health, as their effect on populations
is mediated by factors like physical activity, which can vary from place to place. However,
upstream treatment effect estimates could be biased when mediator variables are missing for the
population where the effect is to be transported. We study this issue of the impact of missing
mediators on transported effects, motivated by challenges in public health, wherein mediators are
commonly missing but not at random. We propose a sensitivity analysis framework to quantify
the impact of missing mediator data on transported mediation effects, identifying when the
conditional transported mediation effect becomes insignificant for subgroups with missing data.
Applied to longitudinal data from the Moving to Opportunity Study, a large-scale housing voucher
experiment, this framework demonstrates the sensitivity of transported mediation effects to data
missingness. In particular, we quantify the effect of missing mediators on transport effect estimates
of voucher receipt in childhood, an upstream intervention on living location. We then assess the
subsequent impact on the risk of mental health or substance use disorder mediated through parental
health across sites. Our findings highlight that missing mediators can disparately impact effect
estimates across population subgroups and provide a tangible understanding of how much missing
data can be withstood for unbiased effect estimates in such mediated settings.

Submission Number: 50