The statistical index
where 
 is the price per unit in period 
, 
 is the quantity produced in period 
, and 
 is the value of the 
 units.
The statistical index
where 
 is the price per unit in period 
, 
 is the quantity produced in period 
, and 
 is the value of the 
 units.
Weisstein, Eric W. "Marshall-Edgeworth Index." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/Marshall-EdgeworthIndex.html