Another amazing example of "Everything is selection".*
This experiment is really neat, so let's go through it.
Facebook users are exposed to more like-minded than cross-cutting news sources. In yellow, you see how this looks for people who were enrolled in this study and in blue, you see daily users in general:
Researchers randomized blinded groups of people to a passive control condition or to receive more exposure from cross-cutting sources. The treatment worked at changing their exposures. Just look:
And then the researchers assessed people's attitudes later on and apparently nothing changed:
Strong attitude-news source exposure associations weren't causal, they were down to selection into the receipt of news sources. Receiving more cross-cutting ones just didn't seem to do all that much.
The researchers described the typical belief:
"Many observers share the view that Americans live in online echo chambers that polarize opinions on policy and deepen political divides. Some also argue that social media platforms can and should address this problem by reducing exposure to politically like-minded content. However, both these concerns and the proposed remedy are based on largely untested empirical assumptions."
But while "Participants in the treatment group were exposed to less content from like-minded sources but were actually more likely to engage with such content when they encountered it." it was also true that "reducing exposure to content from like-minded sources on Facebook had no measurable effect on a range of political attitudes, including affective polarization, ideological extremity and opinions on issues."
The researchers bounded the possible effect between ±0.12 SDs.
Public conversations often feature longwinded discussion of something like this that ends up being a reflection of selection. I assume that will be the case forever, because people appear to think things like social interactions and intuitively important exposures are vital to people's worldviews, even though they're probably not vital to their own.
Ask yourself this: would the generally left-leaning believers in the power of news exposure to change people's views find themselves transformed into right-wingers if they watched Fox News for an hour every day? Would the generally right-leaning believers in, say, QAnon, find themselves transformed into liberals if they watched MSNBC for an hour every day?
If you believe the answers are "yes", you still need to think about selection.
Source:
nature.com/articles/s41586-0…
* More accurately, the majority of 'large' effects are selection.
It would appear people are in echo chambers because they are polarized, not that they are polarized because they are in echo chambers.