The obvious difference was the decisions they made. In the group that had read the article biased in favor of merging the schools, nearly 90 percent favored the merger. In the group that had read the article that was biased by including only information in favor of keeping the schools separate, less than a quarter favored the merger.
The other half of the experimental population wasn't given the survey immediately. Instead, they were given the article that they hadn't read—the one that favored the opposite position of the article that they were initially given. You can view this group as doing the same reading as the control group, just doing so successively rather than in a single go. In any case, this group's responses looked a lot like the control's, with people roughly evenly split between merger and separation. And they became less confident in their decision.
It’s not too late to change your mind
There is one bit of good news about this. When initially forming hypotheses about the behavior they expected to see, Gehlbach, Robinson, and Fletcher suggested that people would remain committed to their initial opinions even after being exposed to a more complete picture. However, there was no evidence of this sort of stubbornness in these experiments. Instead, once people were given all the potential pros and cons of the options, they acted as if they had that information the whole time.
But that shouldn't obscure the fact that there's a strong cognitive bias at play here. "Because people assume they have adequate information, they enter judgment and decision-making processes with less humility and more confidence than they might if they were worrying whether they knew the whole story or not," Gehlbach, Robinson, and Fletcher.
This is especially problematic in the current media environment. Many outlets have been created with the clear intent of exposing their viewers to only a partial view of the facts—or, in a number of cases, the apparent intent of spreading misinformation. The new work clearly indicates that these efforts can have a powerful effect on beliefs, even if accurate information is available from various sources.
PLOS ONE, 2024. DOI: 10.1371/journal.pone.0310216 (About DOIs).