Bias or Diversity? Unraveling Semantic Discrepancy in U.S. News Headlines

There is a broad consensus that news media outlets incorporate ideological biases in their news articles. However, prior studies on measuring the discrepancies among media outlets and further dissecting the origins of semantic differences suffer from small sample sizes and limited scope. In this study, we collect a large dataset of 1.8 million news headlines from major U.S. media outlets spanning from 2014 to 2022 to thoroughly track and dissect the semantic discrepancy in U.S. news media. We employ multiple correspondence analysis (MCA) to quantify the semantic discrepancy relating to four prominent topics - domestic politics, economic issues, social issues, and foreign affairs. Additionally, we compare the most frequent n-grams in media headlines to provide further qualitative insights into our analysis. Our findings indicate that on domestic politics and social issues, the discrepancy can be attributed to a certain degree of media bias. Meanwhile, the discrepancy in reporting foreign affairs is largely attributed to the diversity in individual journalistic styles. Finally, U.S. media outlets show consistency and high similarity in their coverage of economic issues.