Price Controls and Consumer Surplus

The condition for when a price control increases consumer welfare in
perfect competition is tighter than often realised. When demand is linear, a
small restriction on price only increases consumer surplus if the elasticity of
demand exceeds the elasticity of supply; with log-linear or constant-elasticity,
demand consumers are always hurt by price controls. The results are best
understood - and can be related to monopoly-theory results - using the fact
that consumer surplus equals the area between the demand curve and the
industry marginal-revenue curve.