BCA shortcuts:
  1. Linear demand and supply are usually good approximations of nonlinear demand and supply. The sign of the bias is known.
  2. Increases (decreases) in government expenditures are usually good measures of costs (benefits). The price effects are usually small.
  3. Secondary market effects can usually be ignored. When there are price effects, errors in primary market benefits and costs are systematically offset by benefits and costs in secondary markets. When there are no price effects, secondary market effects are either the "dual" choice problem or insignificant.