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.

翻译：新闻媒体在报道中融入意识形态偏见已成为广泛共识。然而，先前关于衡量媒体间差异并进一步剖析语义差异根源的研究存在样本量小、范围有限的问题。本研究收集了2014年至2022年间美国主流媒体180万条新闻标题的大规模数据集，以全面追踪和剖析美国新闻媒体中的语义差异。我们采用多重对应分析（MCA）量化了与四大主题——国内政治、经济问题、社会问题和外交事务——相关的语义差异。此外，我们比较了媒体标题中最常见的n-gram，以提供更具定性的分析见解。研究结果表明，在国内政治和社会问题上，差异在一定程度上可归因于媒体偏见；而在外交事务报道中，差异主要源于个体新闻风格的多样性；最后，美国主流媒体在经济议题报道上表现出一致性和高度相似性。