In this paper we estimate the degree of substitutability for advertisers across different media outlets. The estimates are motivated by the need that competition agencies have to properly characterize the relevant market when dealing with mergers in the media industry. As technology changes the industry, advertisers may not view a given media outlet as independent from those operating in other media platforms. Indeed, our results show that advertisers see outlets across platforms, either as substitutes or complements. From a policy perspective, our findings imply that competition agencies, particularly when defining relevant markets, should not assume that advertisers operate independently within a single media platform.
