Variability of PED along a straight-line demand curve

Elastic portion of the demand curve:

 

• When there is a high price & low quantity demanded → a small percentage change in price leads to a large percentage change in quantity demanded → %ΔQd > %ΔP → PED > 1 → PED is elastic

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Unitary portion of the demand curve:

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• When price and quantity demanded changes by the same percentage → %ΔQd = %ΔP → PED = 1 → PED is unitary elastic

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Inelastic portion of the demand curve:

 

• When there is a low price & high quantity → a large fall in percentage change of price leads to a small rise in percentage change of quantity demanded → %ΔQd < %ΔP → PED < 1 → PED is inelastic