As the name implies, the price elasticity of demand measures the degree to which a quantity of goods or services is responsive to the price of a good or service. We can consider the price elasticity of individual demand (requires responsiveness to the individual quantity of the price) or the market level (requires responsiveness to the market quantity of the price). Mathematically, the price elasticity of demand is equal to the percentage change in the quantity required for a good or service divided by the percentage change in the price of a good or service that produces a change in demand. (Note that the correct price elasticity calculation will include all factors except the price constant change.) Like other elasticity, we can use this formula to calculate point elasticity, or we can use the midpoint formula to calculate the price elasticity of the arc elastic version. . Since the demand law means that the demand curve is almost always tilted downwards (unless Giffen goods are of course good), the price elasticity of demand is almost completely negative. Sometimes, as a rule, the price elasticity of demand is reported as an absolute value (ie, a positive number) and only implies a negative sign. Like other resilience, the price elasticity of demand can be classified as either fully elastic or completely inelastic. If the price elasticity of demand is completely inelastic, then when the price of the commodity changes, the demand for the commodity will not change. (For example, people want the necessary drugs to be an example of such drugs.) Like other elasticity, in this case, the total inelasticity corresponds to the price elasticity of demand equal to zero. If the price elasticity of demand is completely elastic, then even the slightest change in the price of the commodity, the quantity required for the commodity will change substantially indefinitely. In this case, full elasticity corresponds to the price elasticity of the demand of positive or negative infinity, depending on whether or not the convention of reporting the price elasticity of demand as an absolute value is followed.