Why Has Empirical Evidence on Economies of Scale and Scope

Why has empirical evidence on economies of scale and scope been so contradictory?

A) Data on bank costs are unavailable.
B) Efficiency may be related to overall market conditions.
C) Efficiency may be related to non-quantifiable variables such as managerial ability.
D) Neither the intermediation nor the production approach conform to reality.
E) The methodology to detect economies of scale and scope are still very rudimentary.