The Bible indicates that in times of great persecution, true believers who are the "overcomers" loved not their lives unto death so they didn't misstate their beliefs but rather went to their graves holding them. Those who didn't overcome can be broken.
2Ti 2:12 If we suffer, we shall also reign with him: if we deny him, he also will deny us:
Re 12:11 And they overcame him by the blood of the Lamb, and by the word of their testimony; and they loved not their lives unto the death.
Re 3:8 I know thy works: behold, I have set before thee an open door, and no man can shut it: for thou hast a little strength, and hast kept my word, and hast not denied my name.
Because it is extremely important what we say, it would be a good time to bone up on Fox's Book of Martyrs by John Foxe. It is not light reading, but is important in light of the death culture taking over the world which calls good evil and evil good. There are many prophecies in which enemies are requiring Christians to "deny Christ." If you squeeze fruit, you find out what is inside. That may just be a picture of Tribulation as it brings what is inside each person.
I'd guess many more than 80% were broken.