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The Hicksian demand function isolates the substitution effect by supposing the consumer is compensated with exactly enough extra income after the price rise to purchase some bundle on the same indifference curve. [2] If the Hicksian demand function is steeper than the Marshallian demand, the good is a normal good; otherwise, the good is inferior.
A synonymous term is uncompensated demand function, because when the price rises the consumer is not compensated with higher nominal income for the fall in their real income, unlike in the Hicksian demand function. Thus the change in quantity demanded is a combination of a substitution effect and a wealth effect.
where (,) is the Hicksian demand and (,) is the Marshallian demand, at the vector of price levels , wealth level (or income level) , and fixed utility level given by maximizing utility at the original price and income, formally presented by the indirect utility function (,).
It is also possible that the Hicksian and Marshallian demands are not unique (i.e. there is more than one commodity bundle that satisfies the expenditure minimization problem); then the demand is a correspondence, and not a function. This does not happen, and the demands are functions, under the assumption of local nonsatiation.
Roy's identity reformulates Shephard's lemma in order to get a Marshallian demand function for an individual and a good from some indirect utility function.. The first step is to consider the trivial identity obtained by substituting the expenditure function for wealth or income in the indirect utility function (,), at a utility of :
where (,) is the Hicksian demand for good , (,) is the expenditure function, and both functions are in terms of prices (a vector) and utility . Likewise, in the theory of the firm , the lemma gives a similar formulation for the conditional factor demand for each input factor: the derivative of the cost function c ( w , y ) {\displaystyle c ...
The consumer's demand is always to get the goods in constant ratios determined by the weights, i.e. the consumer demands a bundle (, …,) where is determined by the income: = / (+ +). [1] Since the Marshallian demand function of every good is increasing in income, all goods are normal goods .
The Hicksian (per John Hicks) and the Marshallian (per Alfred Marshall) demand function differ about deadweight loss. After the consumer surplus is considered, it can be shown that the Marshallian deadweight loss is zero if demand is perfectly elastic or supply is perfectly inelastic.