where the notation means that the variables to the right of the
vertical line are held constant.
This function is correctly described as the demand function with
respect to price, all other variables being held constant. This
function, often written concisely as , shifts in response
to changes in other variables. Consider average income: If, as is
usually hypothesized, , then increases in average
income shift rightward and decreases in average
income shift leftward. Changes in other variables
likewise shift this function in the direction implied by the
relationship of that variable to the quantity demanded.
3. Quantity demanded is a simple and straightforward but
frequently misunderstood concept in everyday use, but it has a
clear mathematical meaning. It refers to the dependent variable in
the demand function from note 2:
It takes on a specific value whenever a specific value is assigned
to each of the independent variables. The value of changes
whenever the value of any independent variable is changed.
could change, for example, as a result of a change in any one
price, in average income, in the distribution of income, in tastes,QD=d(p)∣∣T,Y ̄ ̄ ̄,N,Yˆ,pjQD=d(p)∂QD/∂ ̄Y ̄ ̄> 0
QD=d(p)
QD=d(p)QD=D(T,Y ̄ ̄ ̄,N,Yˆ,p,pj)QD