Concerning the Reformation and the two big doctrines that came out of it -- sola scriptura (Bible alone) and sola fide (faith alone) -- there was a Pew Research poll done a few years ago, asking U.S. Protestants about whether they ascribed to those beliefs.

Turns out, only 30 percent of U.S. Protestants believe in both sola fide and sola scriptura.

https://www.americamagazine.org/faith/2017/08/31/poll-most-p...