Purchasing power
The Gerschenkron effect, developed by Alexander Gerschenkron, claims that changing the base year for an index determines the growth rate of the index. This effect is applicable only to aggregation method using reference price structure (meaning, each country’s quantities are valued by uniform set of prices to obtain volume) or reference volume structure (meaning, obtaining Purchasing power parity via valuation of uniform set of quantities by each country’s price). However, if production is measured by "real" tearms, this effect does not exist.