In part one of this series, we empirically investigated news bias in the US towards politicians. Our results showed that news bias has indeed grown over the past presidential cycle1. We observed that the rise in bias, most notable at the extremes on the left-to-right political spectrum, was on account of the Left being less positive towards Biden/Harris than the Right was towards Trump, while the Left and Right were equally negative towards Trump and Biden/Harris, respectively.
Here, in part two, we follow the same methodological approach and investigate bias towards the two main political parties in the US. This analysis supports the view that political news in the US is and has become increasingly biased. We find similar results as in part one, with similar, yet some idiosyncratic bias dynamics for political parties.
As a reminder, our proxy for determining bias is sentiment towards political entities extracted from five groups of news sources ranked on the left-to-right political spectrum2. Here, as in part one, we first explore the overall sentiment of news group but towards political parties, and then extend to explore thematic sentiment. We chose five themes: abortion; immigration; crime; economy; and climate.3
For political parties our analysis is extended to the past two decades.
Political Parties: Overall
We extract sentiment (from +1, most positive, to -1, most negative) for the Republican and Democratic parties from each of the news groups. We identify sentiment tilts relative to a benchmark defined as the average sentiment for each party across all news groups. Removing this benchmark from the sentiment for each news group gives us a ‘debased’ sentiment, or, simply, the sentiment deviation of a news group relative to the benchmark. To determine the evolution of bias, we calculate and take the cumulative spread between the two parties. This can be thought of as a ‘bias P&L’, with the slope rather than the level the important measure. Lack of bias will result in a spread of ~0. Our calculation convention for the spread is Republican minus Democratic party, which is to be interpreted as everything below zero being more positive towards the Democratic Party, and anything above zero more positive towards the Republican party – see figure 1 below. This convention is an arbitrary choice, the inverse would yield the exact, but opposite sign and interpretation.
We observe a similar pattern for political parties: overall bias on the Left and Right extremes have increased over the past two decades. However, contrary to politicians, the bias on the Left has increased more towards the Democratic party than bias on the Right has increased towards the Republican party. Moreover, the spread between the parties from Skew Left and Center has remained remarkably balanced, and consistent, more so than for politicians – perhaps counter to anecdotal perception.
Political Parties: Themes
We identify bias or sentiment tilts from the news groups vis-a-vis the five themes (abortion, immigration, crime, economy, and climate) by debasing the themes’ sentiment for the parties using the same method as above. We remove a theme’s average sentiment across all news groups from each of the news groups individually. This yields the deviation of a news group for a particular theme. We again calculate the spread between the parties, remaining consistent with the convention above (arbitrarily choosing <0 as positive towards the Democratic party and >0 as positive towards the Republican party). These thematic sentiment spreads are shown in figure 2.
Again, not too dissimilar when measuring thematic bias towards politicians, we find a pattern that holds with conventional beliefs of Left news sources that lean more positive towards the Democratic party and vice versa. However, there is one major distinction between politicians and political parties: for politicians, the Left and Right spreads were of near-equal but opposite size, while for political parties the Left has become much more biased in favor of the Democratic party than the Right has in favor of the Republican party.
The bias trend from the Left is also more consistent among all themes than the opposing extreme, the Right, and any of the other news media groupings (although the Skew Right comes close). In fact, it is the Skew Right (the likes of Fox Business), more so than the Right (the likes of Fox News) where the biggest bias is observed. Since ~ 2010, this grouping has outpaced the Right and become more positive towards the Republican party on all themes, most notably on climate. And while crime was the source of most bias for politicians, it is climate and abortion that polarizes political parties.
The Skew Left, while being fairly balanced on most themes, has seen a slight bias increase in favor of the Democratic party on the economy and abortion. The Center has remained more balanced, except on abortion where it slightly favors the Republican party.
As in the case for politicians, the Right and Skew Right cluster together more than the Left and Skew Left, this again on account of the Left being systematically (and increasingly) more positive towards the Democratic party than the Skew Left. This supports our initial theory that the Right and Skew Right harbor similar bias on core societal themes, while the extreme bias of the Left is not equally present in the Skew Left.
The biggest bias increase from the Left has been on the climate (followed by abortion and crime). For the Right, the increased bias has been more universal amongst themes.
Key take-aways
1. Overall news bias towards political parties has grown, matching our results for politicians. Likewise, the bias is most notable at the extremes of the political spectrum. However, contrary to the bias towards politicians (where the biggest spread was from the Right), for political parties the biggest spread is from the Left.
2. Overall, there is minimal bias from Skew Left and Center. The common view that the Skew Left (like CNN), and the Center (like CBS) are systematically more in favor towards the Democratic party and its politicians does not seem to be borne out by our analysis.
3. For themes, it is the Skew Right (like Fox Business), more so than the Right (like Fox), that features the higher levels of bias in favor of the Republican party.
4. The Right and Skew Right are consistently more favorable towards the Republican party on all themes, a feature not found in the Left and Skew Left. The bias from the Left and Skew Left cluster less, with the Left systematically more positive towards the Democratic party. This feature was similar for politicians.
5. Our initial theory that the Right and Skew Right harbor similar bias on core societal themes, more so than the Left and Skew Left, seems to be validated given the comparable results found for bias towards political parties. The Left is systematically more biased in favor of the Democratic politicians and party.
1 Part one can be found on our website by following this link.
2 For the groupings we rely on rankings published by media watchdogs in the US. We choose those news sources that have a high degree of communal agreement across the watchdogs; limit to those that are considered ‘mainstream’ or has wide-enough readership; and are deemed to have a high level of reliability. We also limit the choice of news outlet that are US-based.
3 These themes, as was the case in the most recent US presidential election, have consistently been ranked as major concerns for US voters in polls. See for example: https://www.pewresearch.org/politics/2024/09/09/issues-and-the-2024-election/.
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