Price Controls and Consumer Surplus

Price controls lead to misallocation of goods and encourage rent-seeking. The misallocation e¤ect alone is enough to ensure that consumer surplus is always reduced by a price control in an otherwise-competitive market with convex demand if supply is more elastic than demand; or when demand is log-convex (e.g., constant-elasticity) even if supply is inelastic. The same results apply both when rationed goods are allocated by costless lottery among interested consumers, and when costly rent-seeking and/or partial de-control mitigates the allocative ine¢ ciency. The results are best understood using the fact that in any market, consumer surplus equals the area between the demand curve and the industry marginal revenue curve.