Distortions (economics)

A distortion is "any departure from the ideal of perfect competition that therefore interferes with economic agents maximizing social welfare when they maximize their own". A proportional wage-income tax, for instance, is distortionary, whereas a lump-sum tax is not. In a competitive equilibrium, a proportional wage income tax discourages work.

In perfect competition with no externalities, there is zero distortion at market equilibrium of supply and demand where price equals marginal cost for each firm and product. More generally, a measure of distortion is the deviation between the market price of a good and its marginal social cost, that is, the difference between the marginal rate of substitution in consumption and the marginal rate of transformation in production. Such a deviation may result from government regulation, monopoly tariffs and import quotas, which in theory may give rise to rent seeking. Other sources of distortions are uncorrected externalities, different tax rates on goods or income,inflation, and incomplete information. Each of these may lead to a net loss in social surplus.

...
Wikipedia