Researchers want the public to test themselves: https://yourmist.streamlit.app/. Selecting true or false against 20 headlines gives the user a set of scores and a “resilience” ranking that compares them to the wider U.S. population. It takes less than two minutes to complete.
The paper
Edit: the article might be misrepresenting the study and its findings, so it’s worth checking the paper itself. (See @realChem 's comment in the thread).
Got 20/20, was rewarded with a message, “You’re more resilient to misinformation than 100% of the US population!” and looked for the Fake button because as a member of the US population, that is a mathematical impossibility.
Rounding error :)
100% has a margin of error in millions, or tens of, depending on interpretation.
For most purposes, a 5% margin of error is considered acceptable. Since some quick websearch estimates 336M people, this means ~17M people.