Transforming Stability into Change: How the Media Select and Report Opinion Polls

Although political polls show stability over short periods of time, most media coverage of polls highlights recurrent changes in the political competition. We present evidence for a snowball effect where small and insignificant changes in polls end up in the media coverage as stories about changes. To demonstrate this process, we rely on the full population of political polls in Denmark and a combination of human coding and supervised machine learning of more than four thousand news articles. Through these steps, we show how a horserace coverage of polls about change can rest on a foundation of stability.