The supply side of media bias

In my ECONS102 class, we cover economic explanations for media bias. Drawing on past research from Matthew Gentzkow and others, we demonstrate that there are demand-side explanations (media bias arises because of a bias in the preferences of the news-consuming public) and supply-side explanations (media bias arises because media firms segment the market, and focus on different segments). I even shared my teaching approach in this article published in the Journal of Economic Education in 2023 (ungated earlier version here).

I'm always on the lookout for more research in this space, which can add to our understanding (and potentially flesh out more details for my teaching of media bias). One example is this 2024 working paper by Tin Cheuk Leung and Koleman Strumpf (both Wake Forest University). They focus on the supply side of the media market, and their method:

...evaluates the factors which shape article duration on a newspaper’s digital homepage. Homepage articles have a privileged position, as it is the starting point for most readers which in turn drives views and shares of the featured articles. One of the most important editorial decisions is selecting how long each article remains at this prized location. After adjusting for demand-side effects using reader engagement data, we use prolonged homepage presence of ideologically slanted articles as indicative of supply-side biases.

Leung and Strumpf focus on articles in the New York Times (a more liberal media outlet) and the Wall Street Journal (a more conservative media outlet), using data from August 2021 to May 2023 for the NYT, and from October 2022 to May 2023 for the WSJ. They also look at data from Twitter (about 22 million tweets for the NYT sample, and about 2 million tweets for the WSJ sample). First, they use textual analysis to determine the sentiment and political leaning of each article from each of the media outlets. From this, they find:

...a liberal bias in NYT articles, with an average pro-Democrat score of 0.6 (where 1 represents full pro-Democrat alignment and 0 indicates complete pro-Republican alignment), while WSJ articles exhibited more neutrality, with an average score of 0.5.

Next, Leung and Strumpf look an article's presence on the homepage of each media outlet, and how that relates to tweet count (as a proxy measure of the article's popularity). Specifically, they evaluate:

...the causal impact of homepage presence on tweet count, using time-of-day homepage updating patterns as an instrumental variable... There are distinctive hours of the day in which there are large purges of homepage content, likely associated with editor shift changes. These hours occur throughout the day and so are unrelated to article newsworthiness though they do shape which articles are on the homepage. After instrumenting we find that tweet counts for articles increased significantly when featured on the homepage (35% increase for NYT articles and 162% for WSJ articles).

Unsurprisingly then, articles that appear on the homepage are more popular, receiving far more attention from the public. Next, Leung and Strumpf apply survival models to investigate the factors associated with how long an article remains on the media outlet's homepage. First, unsurprisingly, popularity matters:

A key finding from our analysis is the significant impact of demand-side factors. There is a strong negative relationship between tweet counts at t−1 (a proxy for article popularity) and the hazard rate (the likelihood of an article being removed from the homepage). For the NYT, a one standard deviation increase in log tweets (1.37) leads to 2.5% decrease in the hazard rate. This effect is even more pronounced for WSJ, where a one standard deviation in log tweets (1.09) leads to a 10.0% decrease in the hazard rate. This indicates that more popular articles, as measured by tweet counts, tend to remain on the homepage longer, underscoring the role of reader demand in determining homepage duration.

The 'hazard rate' is the rate at which an article is removed from the homepage. So, a lower hazard rate means that the article remains on the homepage for longer. The demand side (popularity) matters, but the supply side matters as well:

Supply-side factors are particularly influential for the NYT. A one-standard-deviation increase in an article’s pro-Democrat score, indicating its political slant, is associated with a 2% decrease in the hazard rate, which translates into approximately an additional 30 minutes of homepage exposure. This relationship holds across different news tones, suggesting that a wide range of NYT’s editorial decisions on homepage duration are influenced by the article’s political alignment....

For the WSJ, the influence of supply-side factors is generally negligible, both overall and for each news tone. The pro-Democrat scores of articles do not significantly affect their duration on the homepage, contrasting with the NYT, where political slant plays a noticeable role.

So, the NYT's approach to its homepage is affected by the supply side, but the WSJ's approach is not. Leung and Strumpf suggest that:

This suggests that the WSJ might prioritize profit-maximizing objectives over ideological considerations (recall demand-side effects are also larger for the WSJ).

That would be consistent with the models I teach in my ECONS102 class. A profit-maximising media firm should base its' decision about where to locate its content on the liberal-conservative scale based on the relative demand from the news-consuming public, and not at all based on the editorial preferences of the owners or editors. Leung and Strumpf are essentially suggesting that this is true of the WSJ, but not the NYT.

Interestingly though, sentiment matters as well:

The sentiment of an article, captured through abstract sentiment scores, is notably linked to its duration on the homepage. For the NYT, a one standard deviation increase in the abstract sentiment scores is associated with a 2% decrease in the hazard rate, indicating that more positively toned articles are likely to remain on the homepage longer. The effect is even more pronounced for the WSJ, where a similar increase in sentiment scores corresponds to a 4% decrease in the hazard rate.

Whatever happened to 'if it bleeds, it leads'? Since more positively framed news stays on the homepage for longer, that old mantra may be on the way out. Overall, it seems that both demand and supply sides affect which articles receive prominence on the homepage of the NYT, and that for the WSJ it is mostly the demand side. In the latest version of their paper [*], Leung and Strumpf conclude by noting the importance of understanding the supply side of media bias, in an era when local newspapers are closing, increasing the risk of media bias.

[HT: Marginal Revolution, last year]

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[*] In the January 2024 version of the paper, which is the one I read some time back, Leung and Strumpf had clearly used ChatGPT (or some other LLM) to write the conclusion, with hilarious results, including a 'rich tapestry', a 'symbiotic relationship', an 'intricate balance', a 'multifaceted realm', 'delving', and a 'deep dive'. Thankfully, the latest version appears to have resolved this issue.