The elasticity coefficient is a number that indicates the percentage change that will occur in one variable (y) when another variable changes one percent.
It is defined as the ratio:
If y is quantity demanded and x is price, then the ratio represents the price-elasticity coefficient, which indicates the percentage change in quantity as price changes 1%. If x is income then the number becomes the income-elasticity coefficient.
Price elasticity is important in business to determine in a given market whether an increase (or decrease) in prices will generate an increase (or decrease) in revenues.
The following cases are possible for the price elasticity coefficient (given that the relationship between quantity demanded and price is expected to be negative, we focus on the absolute value of the elasticity coefficient).