The size of investment multiplier (k) depends on:-

Marginal propensity to consume

Investment multiplier refers to the increase in the aggregate income of the economy as a result of an increase in the investments done by the government.  The ratio of ΔY to ΔI is called the investment multiplier.

K = \(\frac{ΔY}{ΔI}\) 

K = \(\frac{1}{\text{1-MPC}}\)  = \(\frac{1}{\text{MPS}}\)

Thus, according to the question, we can say that size of the investment multiplier depends on the "Marginal propensity to consume."