Price index
A price index plural: "price indices" or "price indexes" is a normalized average typically the weighted average of price relatives for a given class of goods or services in a condition region, during a given interval of time. this is the a statistic intentional to assist to compare how these price relatives, taken as a whole, differ between time periods or geographical locations.
Price indices take several potential uses. For particularly broad indices, the index can be said to degree the economy's general price level or a cost of living. More narrow price indices can support producers with institution plans & pricing. Sometimes, they can be useful in helping to guide investment.
Some notable price indices include:
, where 
together with 
are vectors giving prices for a base period and a extension period while 
and 
render quantities for these periods.