Practical uses of supply and demand analysis often center on the different variables that change equilibrium price and quantity, represented as shifts in the respective curves. Comparative statics of such a shift traces the effects from the initial eqilibrium to the new equilibrium.
People increasing the quantity demanded at a given price are referred to as an increase in demand. Increased demand can be represented on the graph as the curve being shifted outward. At each price point, a greater quantity is demanded, as from the initial curve D1 to the new curve D2. More people wanting coffee is an example. In the diagram, this raises the equilibrium price from P1 to the higher P2. This raises the equilibrium quantity from Q1 to the higher Q2. A movement along a given demand curve can be described as a "change in the quantity demanded" to distinguish it from a "change in demand," that is, a shift of the curve. In the example above, there has been an increase in demand which has caused an in increase in (equilibrium) quantity. The increase in demand could also come from changing tastes, incomes, product information, fashions, and so forth.
When the suppliers' costs change for a given output, the supply curve shifts in the same direction. For example, assume that someone invents a better way of growing wheat so that the cost of wheat that can be grown for a given quantity will decrease. Otherwise stated, producers will be willing to supply more wheat at every price and this shifts the supply curve S1 outward, to S2—an increase in supply. This increase in supply causes the equilibrium price to decrease from P1 to P2. The equilibrium quantity increases from Q1 to Q2 as the quantity demanded increases at the new lower prices. In a supply curve shift, the price and the quantity move in opposite directions.