1. A method of generating a list of parameter value combinations to test, the method comprising: (a) providing to a user a graphical user interface that includes at least two adjustable probability curves that allow the user to graphically indicate the importance of values of at least first and second parameters; (b) converting the probability curves into probability functions; (c) combining the probability functions into a combination function; and (d) selecting parameter value combinations that result in the combination function exceeding a predetermined probability value.