A practical approach to choosing formulae for economic index numbers

Traditional axiomatic, economic and stochastic approaches to choosing a formula for economic index numbers are based on theoretical considerations, with little regard to whether they reflect the actual circumstances affecting the markets to which they relate. This paper presents an approach to index number formulation based on how markets operate and presents a general, parameter-based formula for price and quantity indices. Two variants of this general formula cater for the “substitution effect” in different ways and one of these variants provides a practical expression for an economic-theoretic index based on purchasers' revealed preferences. Another variant applies this approach to short-term inflation indices. A final variant provides a straightforward means of estimating purchasing power parities for spatial indices. The analysis also emphasizes the importance of using coherent price and quantity indices, whose products generate the corresponding value indices.