- loss of information. For example, aggregation suppresses the fact
that alternative A has environmental effects, whereas alternative B has financial
- subjective weighting of different aspects. Unfortunately, these
crucial weights and assumptions are often implicit or highly speculative.
They may impose to the decision makers a value scheme bearing little relation
to their concerns. For example, cost-benefit analysis implicitly assumes that
a dollar's worth of one kind of benefit has the same value as a dollar's worth
of another. Yet in many public decisions, monetary equivalent but otherwise
dissimilar benefits would be valued differently by society.
- impossibility to aggregate for several clients with different points
of view. The aggregate techniques are intended to help an individual decision
maker in selecting the preferred alternative, the one that best reflects his
values (importance weights). Serious theoretical and practical problems arise
when there are multiple decision makers: Whose values should be used (the
issue of inter-personal comparison of values), and what relative weight does
the group give to the preferences of different individuals (the issue of equity)?
- assumption of independence effects. The aggregate technique (others
than cost-benefit analysis) requires that the importance (value) of each effect
be independent of the size of all other effects. But in the real world, this
condition is not always satisfied. Each effect that violates this condition
must be suppressed, either by eliminating it or by treating is at the next
level of aggregation.