Function to generate a score out of 100% based on other parameters

Question

I am attempting to score an outcome out of 100%, which will be an evaluation of "risk" level.

The factors would be (for example):

• if number of users increases, risk level increases
• if secure protocol is used risk level decreases vs unsecured

• if particular configuration is used (say, out of 3 possible - each carrying a "factor" of i.e. 1, 2, 3

  1. What is the general branch or area of mathematic that deals with this?
  2. How would I go about evaluating for this particular example (feel free to make up factors or values.. or even. point me to an example)

my problem is, I'm not quite sure what to search for...