There is no neat, mechanical formula that is followed nor can a computer model predict the thought process a Member goes through in arriving at a vote. Policy arguments do not always persuade. Political pressures are often withstood. Campaign contributions are not always rewarded. Public opinion is always gauged but not always followed.
Members consult their consciences, but sometimes cede to the majority perspective.
The decision-making process that precedes casting a vote is often lengthy and complex and known fully only to the Member going through it. And as they vote, each Member knows that in our democracy they alone will be held accountable for the decision they are about to make.