What influences the AI's decision to change religion?

[Uliono]

As the title says, I can't seem to find an explanation of what influences the AI's decision to become Protestant or Reformed and in my games it often seems rather random. Sometimes countries will spontaneously convert after one province become Protestant, and other times they will stubbornly hold out as Catholic despite being mostly Protestant or Reformed. Anyone know what causes these decisions?

 

[ChildeR]

I don't know all the factors, but the first few to get a reformation events will ~always convert because they get a center of reformation. After all the centers have appeared they are less likely to convert for any reason.