consequences. Price elasticity of demand The price elasticity of demand is a measure of the sensitivity of the quantity variable, Q, to changes in the price variable, P. It shows the percent by which the quantity demanded will change as a result of a given percentage change in the price. Thus, a demand elasticity of -2 says that the quantity demanded will fall 2% if the price rises 1%. For infinitesimal changes, the elasticity is (∂Q/∂P)×(P/Q). Elasticity along linear demand curve The slope of a linear demand curve is constant. The elasticity of demand changes continuously as one moves down the demand curve because the ratio of price to quantity continuously falls. At the point the demand curve intersects the y-axis, demand becomes infinitely elastic, because the variable Q appearing in the denominator of the elasticity formula is zero. At the point the demand curve intersects the x-axis, the elasticity is zero, because the variable P appearing in the numerator of the elasticity formula is zero. At one point on a linear demand curve, demand is unitary elastic: an elasticity of one. For higher prices, the elasticity is greater than 1 in magnitude: demand is said to be elastic because percentage quantity changes are bigger than price changes. For prices below the point of unit elasticity, the elasticity is less than 1 and demand is said to be inelastic. Constant price elasticity demand Constant elasticity of demand occurs when where a and c are parameters, and the constant price elasticity is Perfectly inelastic demand Perfectly inelastic demand is represented by a vertical demand curve. Under perfect price inelasticity of demand, the price has no effect on the quantity demanded. The demand for the good remains the same regardless of how low or high the price. Goods with (nearly) perfectly inelastic demand are typically goods with no substitutes. For instance, insulin is nearly perfectly inelastic. Diabetics need insulin to survive so a change in price would not effect the quantity demanded. Insulin is not perfectly inelastic, however, as a prohibitively high price would cause some individuals to be incapable of purchasing insulin entirely. On the other hand, if insulin was sold at a very low price, it is possible that some individuals would purchase more insulin if they were not able to afford it before. Because of the effects of extreme pricing, no good can be considered truly perfectly inelastic. Market