  We introduce a family of normative principles to assess fairness in the
context of participatory budgeting. These principles are based on the
fundamental idea that budget allocations should be fair in terms of the
resources invested into meeting the wishes of individual voters. This is in
contrast to earlier proposals that are based on specific assumptions regarding
the satisfaction of voters with a given budget allocation. We analyse these new
principles in axiomatic, algorithmic, and experimental terms.
