The correct answer is, it’s complicated. (Of course) It depends greatly on the definition of the output, for example, which can vary by application.

Easy answer is, for a fixed load (I.e. a resistor) and frequency, one varies amplitude with power. (perhaps absolute value of area under the curve might be a better description)

For more information see here: http://hyperphysics.phy-astr.gsu.edu/hbase/Waves/powstr.html This is for a physical string, which I think is easier to wrap your head around. The math is very similar for electrical waves.