What is "Scenario Analysis" of decision making methods ?

Scenario analysis is when you estimate the consequences of all possible decisions in a particular situation.   For example, your choices might be to do X, Y, Z or nothing.  Consider what would happen if you do X, what would happen if you do Y and so on.  You might discover that Y and Z boil down to the same thing, leaving you with3 choices - X, Y, or nothing - and an expected outcome for each one.  This can make it easier to decide which to choose.