负的边际消费倾向？真的吗

我也不太明白了，楼主,希望斑主能详细解释一下. 为什么可能是负数呢?

MPC=dC/dY,for this formula, use the Mathematical way to exaplain the MPC function is expressed as the derivative of the consumption (C) function with respect to disposable income (Y). in the other word, MPC is measured as the ratio of the change in consumption to the change in income, thus giving us a figure between 0 and 1 under the condition if the subject did not borrowed money to finance expenditures higher than their income.

on the other hand, because one minus the MPC equals the MPS. in this case, we can not conclude that MPC<0.