Editing Price index (section)

===== Törnqvist index =====
{{Main|Törnqvist index}}
A [[geometric mean]] weighted by average value shares:<ref>PPI manual, p. 610</ref><ref>[http://www2.stats.govt.nz/domino/external/omni/omni.nsf/wwwglsry/tornqvist+index+and+other+log-change+index+numbers "Tornqvist Index"] {{Webarchive|url=https://web.archive.org/web/20131224111339/http://www2.stats.govt.nz/domino/external/omni/omni.nsf/wwwglsry/tornqvist+index+and+other+log-change+index+numbers|date=24 December 2013}}</ref>

: <math>P_{T} = \prod_{i=1}^{n} \left(\frac{p_{i,t}}{p_{i,0}}\right)^{\frac{1}{2} \left[\frac{p_{i,0} \cdot q_{i,0}}{\sum (p_{0} \cdot q_{0})} + \frac{p_{i,t} \cdot q_{i,t}}{\sum (p_{t} \cdot q_{t})}\right]}</math>

It weights price relatives by economic importance (average expenditure shares), providing precision over Marshall-Edgeworth’s simpler averaging, but it’s data-intensive, needing detailed expenditure data.<ref>PPI manual, p. 610</ref>