Final answer:
The statement 'Adding a common outcome to both options shouldn't change the ordering of preferences' reflects the Axiom of independence in rational choice theory.
Step-by-step explanation:
The statement 'Adding a common outcome to both options shouldn't change the ordering of preferences' reflects the Axiom of independence in rational choice theory. This axiom states that the preferences between two options should not be influenced by the addition or removal of a third option that has no impact on the outcome. In other words, the relative ranking of options should remain unchanged when an irrelevant option is introduced.