Perfectly Inelastic Demand

Price elasticity of demand (PED) measures the responsiveness of demand for a good to a change in its price. It is given by the formula of:

PED = (% of change in quantity demanded) / (% of change in price)

We have 5 types of PED namely elastic in demand (price sensitive), inelastic in demand (less price sensitive) and perfectly inelastic in demand (NOT price sensitive at all)

The other two, unitary elasticity (PED = 1) and perfectly elastic in demand (PED = ∞) are true only in their mathematical property. In reality we don’t really come across goods and services that have similar percentage of change as its price (50% / -50% or -40% / +40%). The same goes for the latter. We will not come across situation where PED = 5000 (+50% / -0.01%)

For the discussion, I’m only concern with PED = 0. Many asked me if there is such good where it is not responsive to price AT ALL? The demand curve is vertical and as such parallel to price axis. The closest example to this will be collectible items or portrait of Mona Lisa. No matter how the prices change, people will only demand for one original portrait of hers because there is only one in the world

Another would be the case for organ transplant. No matter how low or how high is the price, a heart patient will only demand for one heart. So the demand curve stays put