The first part is very int utive. The source has no incent ive to reveal negat ive informa- t ion since his payoff depends on the public having a posit ive perception. The second result clearly follows from Proposition 5. By giving the first newspaper the story, the source maximally benefits from the piling on effect. Later newspapers spin stories consistent with his init ial message. Proposit ion 5 and 6 fo cus on cases with no ideological compet it ion, where newsp pers passively accept the early spin because they have no ideologies of their own. The following proposit ion shows t hat when newspapers' ideologies are very different, the incent ive for newspapers to pile on to the early spin falls Proposition 7 Suppose the number of n ewspapers wi th a positive ideology equals the number with a n egative ideology and that agen ts are categorical thinkers. As the stre of ideologies(B)increases, newspapers'in cen tives to spin stories decreases and the total amount of bias in reporting decreases Proposit ion 7 is perhaps the crucial result of the paper. It shows that newspaper ideol ogy, far from being a problem to be lamented, is in fact crucial for accuracy in media. Wit deological diversity, spin causes newspapers to pile on, and to sacrifice accu racy in order to report memorable stories. When newspapers have different ideologies, however, the competit ive pressures to follow the leader are countered by the pressures of ideology. Ideological diversity is an ant idote to spin 4 Case studies These result s about media bias can be crisply illustrated in two case studies. The first, involv ing NBa star Allen Iverson, highlight s how non-ideological media out s spin stories to be consistent with pre-exist ing categories. The second, involving academics Lawrence Summers and Cornel West, illustrates how ideological bias of newspapers can undo the effects of spin. Each of these examples also gives a sense of the exact mechanisms through which newspapers bias storiesThe rst part is very intuitive. The source has no incentive to reveal negative informa￾tion since his payo depends on the public having a positive perception. The second result clearly follows from Proposition 5. By giving the rst newspaper the story, the source maximally benets from the piling on eect. Later newspapers spin stories consistent with his initial message. Proposition 5 and 6 focus on cases with no ideological competition, where newspa￾pers passively accept the early spin because they have no ideologies of their own. The following proposition shows that when newspapers' ideologies are very dierent, the incentive for newspapers to pile on to the early spin falls. Proposition 7 Suppose the number of newspapers with a positive ideology equals the number with a negative ideology and that agents are categorical thinkers. As the strength of ideologies () increases, newspapers' incentives to spin stories decreases and the total amount of bias in reporting decreases. Proposition 7 is perhaps the crucial result of the paper. It shows that newspaper ideol￾ogy, far from being a problem to be lamented, is in fact crucial for accuracy in media. Without ideological diversity, spin causes newspapers to pile on, and to sacrice accu￾racy in order to report memorable stories. When newspapers have dierent ideologies, however, the competitive pressures to follow the leader are countered by the pressures of ideology. Ideological diversity is an antidote to spin. 4 Case Studies These results about media bias can be crisply illustrated in two case studies. The rst, involving NBA star Allen Iverson, highlights how non-ideological media outlets spin stories to be consistent with pre-existing categories. The second, involving academics Lawrence Summers and Cornel West, illustrates how ideological bias of newspapers can undo the eects of spin. Each of these examples also gives a sense of the exact mechanisms through which newspapers bias stories. 16