Advertising elasticity of demand is the change in sales that results from each monetary unit (e.g. each pound or dollar) that is spend on advertising. It is a similar measure to other elasticities such as price elasticity and is:
(ΔQ)/(Q)÷(ΔA)/(A)
where Q is the quantity sold
A is the advertising expenditure
ΔQ is the change in quantity sold and
ΔA is the change in advertising expenditure