Model Appendix: Ideological Segregation Online and Offline

The analysis in the paper suggests that (i) if news sites were less vertically differentiated, segregation would increase considerably, and (ii) if users did not visit multiple sites, more users would have extremely high or low conservative exposure. To make these hypotheses more precise, we specify and estimate a simple model of Internet news demand, and use it to simulate segregation and conservative exposure under various counterfactual assumptions. We assume that the number of days in the year on which consumer i will visit at least one news site is drawn from a discrete distribution η . On each day consumer i visits at least one news site, the number of visits she makes, κi ∈ {1, ...K}, is drawn from a discrete distribution π . The number of days is drawn independently across consumers and the number of visits is drawn independently across consumers and days. Consumer i’s utility from choosing online outlet j on visit k is