I have a Macbeth project, due, and one of the questions says Do a CAF/PMI for Macbeth to decide whether or not to murder Duncan. Include a paragraph explaining the rationale for either murdering Duncan or not.

My question, is how exactly do I do this, as in I don't know what I'm supposed to do for the CAF/PMI, given I only know that CAF = consider all factors, and I don't know what PMI stands for. And I don't know how to write either one out. Any help is appreciated.
(please don't post if you don't know what your talking about though, it's rather important I get a good mark on this.