On the Potential for Discrimination via Composition

Abstract

The success of platforms such as Facebook and Google has been due in no small part to features that allow advertisers to target ads in a fine-grained manner. However, these features open up the potential for discriminatory advertising when advertisers include or exclude users of protected classes---either directly or indirectly---in a discriminatory fashion. Despite the fact that advertisers are able to compose various targeting features together, the existing mitigations to discriminatory targeting have focused only on individual features; there are concerns that such composition could result in targeting that is more discriminatory than the features individually. In this paper, we first demonstrate how compositions of individual targeting features can yield discriminatory ad targeting even for Facebook's restricted targeting features for ads in special categories (meant to protect against discriminatory advertising). We then conduct the first study of the potential for discrimination that spans across three major advertising platforms (Facebook, Google, and LinkedIn), showing how the potential for discriminatory advertising is pervasive across these platforms. Our work further points to the need for more careful mitigations to address the issue of discriminatory ad targeting.