Residual demand estimation for market delineation: Complications and limitations

To shed some light on market delineation in an antitrust context, many economists are turning to estimates of residual demand elasticities. Recent papers have drawn attention to the importance of demand curve in market delineation and explained how they can be estimated. This paper shows that there are many complications and limitations of the approach. The relationship between the residual demand elasticity and the scope of the relevant market is complicated and depends on behavioral assumptions. The residual demand elasticity that can be estimated is not the one on which market delineation turns. The estimation of residual demand elasticities can be very difficult because of the complex dynamics of consumer behavior. Finally, residual demand estimators are likely to have a high variance because of instrument problems and this is likely to lead to widely varying estimates depending on specification choices.