Question 1

Is the gradient of the demand curve the same as its elasticity?

Accepted Answer

No. This is a common misconception. While a steeper curve is generally more inelastic than a flatter one, elasticity is not constant along a straight-line demand curve, whereas the gradient is. Gradient measures absolute change (rise/run), while elasticity measures percentage change (%ΔQd / %ΔP). The percentage change calculation depends on the starting price and quantity, which is why PED varies at different points on the curve.

Question 2

Why do economists ignore the minus sign when interpreting PED values?

Accepted Answer

The negative sign is a natural consequence of the law of demand (price and quantity demanded are inversely related). By convention, economists use the absolute (positive) value to avoid confusion when comparing elasticities. It is more intuitive to say a PED of 2 is 'more elastic' than a PED of 0.5, rather than comparing -2 and -0.5, where -0.5 is mathematically the larger number.

Question 3

Can a single product have just one PED value?

Accepted Answer

Not usually in the real world. A single PED value given in a textbook or exam is an estimate for a specific price range at a particular point in time. In reality, the PED for a product changes at different price points (as shown by the straight-line demand curve model). Furthermore, it can change over time as new substitutes emerge, consumer incomes change, or tastes and preferences evolve. Therefore, PED is a dynamic, not a static, measure.

Price elasticity of demand

What you need to know

Price elasticity of demand