On the Use of Proxies in Political Ad Targeting

TL;DR

This paper investigates how political advertisers bypass platform restrictions by using proxy attributes for targeting, revealing the scale and effectiveness of such proxies in political ad targeting.

Contribution

It introduces novel methods to measure and analyze the use of proxy attributes in political ad targeting, highlighting their role in circumventing platform mitigations.

Findings

Political advertisers effectively use proxy attributes to target voters.

Proxy attributes closely align with political and racial divides.

The scale of proxy attribute use is significant and widespread.

Abstract

Detailed targeting of advertisements has long been one of the core offerings of online platforms. Unfortunately, malicious advertisers have frequently abused such targeting features, with results that range from violating civil rights laws to driving division, polarization, and even social unrest. Platforms have often attempted to mitigate this behavior by removing targeting attributes deemed problematic, such as inferred political leaning, religion, or ethnicity. In this work, we examine the effectiveness of these mitigations by collecting data from political ads placed on Facebook in the lead up to the 2022 U.S. midterm elections. We show that major political advertisers circumvented these mitigations by targeting proxy attributes: seemingly innocuous targeting criteria that closely correspond to political and racial divides in American society. We introduce novel methods for directly measuring the skew of various targeting criteria to quantify their effectiveness as proxies, and then examine the scale at which those attributes are used. Our findings have crucial implications for the ongoing discussion on the regulation of political advertising and emphasize the urgency for increased transparency.