In economics, tax incidence is the analysis of the effect of a particular tax on the distribution of economic welfare. Tax incidence is said to "fall" upon the group that ultimately bears the burden of, or ultimately has to pay, the tax. The key concept is that the tax incidence or tax burden does not depend on where the revenue is collected, but on the price elasticity of demand and price elasticity of supply. The concept was brought to attention by the French Physiocrats and in particular François Quesnay who argued that the incidence of all taxation falls ultimately on landowners and is at the expense of land rent. For this reason they advocated the replacement of the multiplicity of contemporary taxes by the Impôt Unique, which is similar to what would later be known by Georgists as a 'Single-Tax' on land value. A leading advocate of this tax was Turgot. Physiocrats were correct in their analysis of the tax incidence of land value tax, that it benefits society and falls entirely on landlords. However, they were incorrect in believing that the entire incidence of those indirect taxes would fall on landowners. Even though the incidence of taxes on activities such as consumer sales or employment will lower land values indirectly, maybe by even more than the value of the original tax, some excess burden is likely to also fall on consumers and producers.Initially, the incidence of all labour related taxes such as income tax and mandatory pension contributions falls on employers. This must be so at the margin since the employee must receive more net of tax i.e. take-home than they can receive from the alternative, such as welfare benefit payments. The tax surcharge may be as high as 80%.[citation needed]The theory of tax incidence has a number of practical results. For example, United States Social Security payroll taxes are paid half by the employee and half by the employer. However, some economists think that the worker is bearing almost the entire burden of the tax because the employer passes the tax on in the form of lower wages. The tax incidence is thus said to fall on the employee.