34 percent blame Twitter. The study found that Americans encounter incivility, on average, 17.1 times per week, or 2.4 times per day. Some studies suggest that uncivil communication may have real consequences, including increased health problems due to stress, decreased work productivity, more auto accidents caused by aggressive driving, and vandalism. Political incivility Political incivility is different from the everyday incivility described above. According to face negotiation theory, politeness norms require us to avoid challenging others, but political incivility is different because, since it is specific to the political sphere, contestation of views and confrontation are required for a democracy to occur. According to Thomas Benson, "Where there is disagreement, there is a risk of incivility; in many cases, incivility is itself a tactic in political discourse, employed as an indicator of sincerity, as the marker of the high stakes in a disagreement." Civil discourse is "the free and respectful exchange of different ideas". Eight out of 10 Americans believe that the lack of civil discourse in the political system is a serious problem. Eighty-two percent of American respondents to a 2011 survey felt that political advertisements were too "nasty" and 72 percent believed that political commercials that attacked the opponent were "inappropriate". Research has linked political incivility to reduced trust in the legitimacy of political candidates, political polarization, and policy gridlock. Campaigns and politicians are not the only avenues for incivility, however. The public also participates in civil discourse, and incivility. Incivility in these contexts can lead to the breakdown of political discourse, and exclude certain people or groups from the discussion. If people or groups are systematically excluded from the discussion, the democratic nature of that discussion is called into question. In his article The Public Sphere: An Encyclopedia Article (1964), Habermas explains that the public sphere is "a realm of our social life in which something approaching public opinion can be formed… Although state authority is so to speak the executor of the political public sphere, it is not a part of it." Political incivility threatens the features of the rhetorical model of the public sphere, which include: It is discourse-based as opposed to class-based. Norm of reasonableness, meaning the success of an argument depends on participants agreeing that it makes sense. It "emphasizes indeterminate bracketing of discursive exchanges", meaning the public sphere is made up of many smaller conversations that happen independently of each other. Values