Editing Demand curve (section)

==Shift of a demand curve==
The shift of a demand curve takes place when there is a change in any non-price determinant of demand, resulting in a new demand curve.<ref name="Case, K.E. 1994">{{cite book |last1=Case |first1=K. E. |last2=Fair |first2=R. C. |year=1994 |chapter=Demand, Supply, and Market Equilibrium |title=Principles of Economics |edition=3rd |publisher=Prentice Hall |location=Englewood Cliffs, New Jersey |isbn=0-13-039950-7 }}</ref> Non-price determinants of demand are those things that will cause demand to change even if prices remain the same&mdash;in other words, the things whose changes might cause a consumer to buy more or less of a good even if the good's own price remained unchanged ([[Exogeny|exogenous]] changes).<ref>{{cite web|url=http://www.harpercollege.edu/mhealy/eco212i/lectures/s&d/s&d.htm|title=Demand and Supply|website=www.harpercollege.edu}}</ref>

Some of the more important factors are the prices of related goods (both [[substitute good|substitutes]] and [[complementary good|complements]]), income, population, and expectations. However, demand is the willingness and ability of a consumer to purchase a good ''under the prevailing circumstances''; so, any circumstance that affects the consumer's willingness or ability to buy the good or service in question can be a non-price determinant of demand. As an example, weather could be a factor in the demand for beer at a baseball game.

When [[income]] increases, the demand curve for [[normal goods]] shifts outward as more will be demanded at all prices, while the demand curve for [[inferior goods]] shifts inward due to the increased attainability of superior substitutes (the demand decrease for each price). When a good is a [[neutral good]] its demand want change by a change of income. 

With respect to related goods, when the price of a good (e.g. a hamburger) rises, the demand curve for [[Substitute good|substitute goods]] (e.g. chicken) shifts out, while the demand curve for [[Complementary good|complementary goods]] (e.g. ketchup) shifts in (i.e. there is more demand for substitute goods as they become more attractive in terms of value for money, while demand for complementary goods contracts in response to the contraction of quantity demanded of the underlying good).<ref name="Case, K.E. 1994" />

With factors of individual demand and market demand, both complementary goods and substitutes affect the demand curve.

*Complementary goods are goods A and B where the demand for the former and the price of the latter have an inverse relationship, with an increase in the price of the former leading to a decrease in the demand for the latter and vice versa, but there is no relationship between them as capital goods and consumer goods.
*Substitutes are those goods for which there is a positive relationship between the demand for good A and the price of good B (e.g., an increase in the price of one good is an increase in the demand for the other) and which are in competition with each other.

===Factors affecting individual demand===
* Changes in the prices of related goods (substitutes and complements)
* Changes in [[Disposable/Discretionary income|disposable income]], the magnitude of the shift also being related to the [[income elasticity of demand]].
* Changes in tastes and preferences. Tastes and preferences are assumed to be fixed in the [[short-run]]. This assumption of fixed preferences is a necessary condition for aggregation of individual demand curves to derive market demand.
* Changes in expectations.<ref name="krugman et al."/>{{rp|61–62}}

===Factors affecting market demand===
In addition to the factors which can affect individual demand there are three factors that can cause the market demand curve to shift:

* a change in the number of consumers,
* a change of tastes among consumers,
* a change in the distribution of income among consumers with different tastes.<ref>{{cite book |last1=Binger |first1=B. |last2=Hoffman |first2=E. |title=Microeconomics with Calculus |edition=2nd |publisher=Addison-Wesley |year=1998 |isbn=0-321-01225-9 |quote=A change in relative price changes the distribution of income which in turn changes the demand curve }}</ref>

Some factors which increase the demand (the demand increase for every price - a shift of the demand curve to the right) 
*Decrease in price of a substitute
*Increase in price of a complement
*Decrease in income if good is normal good
*Increase in income if good is inferior good