A graphical representation of the three rules emerging from the plus and minus rules. The highlighted nodes represent the ‘successes’ identified by the corresponding rule. a, The plus-plus rule-if MP1 and MP2 or MP3, then GO1. b, The minus-minus rule-if MP1 and not either MP2 or MP3, then GO1. c, The plus-minus rule-if MP1 and MP2 and not MP3, then GO1.