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