The multiplier discussion lacks sound theoretical foundations. The most elementary version of the correct Employment Law for the economy as a whole is given on Wikimedia AXEC62:
— An increase in the expenditure ratio ρE≡C/Y leads to higher employment.
— An increase in the factor cost ratio ρF≡W/PR leads to higher employment.
The complete Employment Law is a bit longer and contains in addition profit distribution, public deficit spending, and import/export. The Law contains only measurable variables and is testable. This should end the groping in the dark and the inconclusive wish-wash.
#1 The Three Fatal Mistakes of Yesterday Economics: Profit, I=S, Employment