Amoroso–Robinson relation

The Amoroso–Robinson relation, named after economists Luigi Amoroso and Joan Robinson, describes the relation between price, marginal revenue, and price elasticity of demand.

$$\frac{\partial R}{\partial x}=p\left( 1+\frac{1}{\epsilon _{x,p}}\right)$$,

where
 * $$\scriptstyle \frac{\partial R}{\partial x}$$ is the marginal revenue,
 * $$x$$ is the particular good,
 * $$p$$ is the good's price,
 * $$\epsilon_{x,p}<0$$ is the price elasticity of demand.

Extension and generalization
In 1967, Ernst Lykke Jensen published two extensions, one deterministic, the other probabilistic, of Amoroso–Robinson's formula.