 The difference is attributable to the behavioral changes induced by a distortionary tax that are measured by a substitution effect.However, that is not the only interpretation, and Lind and Granqvist (2010) point out that Pigou did not use a lump sum tax as the point of reference to discuss deadweight loss (excess burden).When a tax is levied on buyers, the demand curve shifts downward in accordance with the size of the tax.