If in Doubt, Treat'em Equally

Presumption of Equality requires that individuals be treated equally in the absence of relevant information that would discriminate between them. Our objective is to make this principle more precise, if viewed as a principle of fairness, and to determine why and under what conditions it should be obeyed.
Presumption norms are procedural constraints, but their justification can be sought in the possible or expected outcomes of the procedures they regulate. This is the avenue pursued here. The suggestion is that in the absence of information that would discriminate between the individuals, equal treatment minimizes the expected unfairness of the outcome. A related suggestion is that equal treatment under these circumstances also minimizes the maximal possible unfairness of the outcome. Whether these suggestions are correct or not depends on the properties of the underlying unfairness measure. The required properties are specified.