gk {PriceIndices}

Calculating the multilateral Geary-Khamis price index

Description

This function returns a value of the multilateral Geary-Khamis price index.

Usage

gk(data, start, end, wstart = start, window = 13)

Arguments

data

The user's data frame with information about sold products. It must contain columns: time (as Date in format: year-month-day,e.g. '2020-12-01'), prices (as positive numeric), quantities (as positive numeric) and prodID (as numeric, factor or character).

start

The base period (as character) limited to the year and month, e.g. "2020-03".

end

The research period (as character) limited to the year and month, e.g. "2020-04".

wstart

The beginning of the time interval (which is used by multilateral methods) limited to the year and month, e.g. "2020-01".

window

The length of the time window (as positive integer: typically multilateral methods are based on the 13-month time window).

Value

This function returns a value of the multilateral Geary-Khamis price index which considers the time window defined by wstart and window parameters. The Geary-Khamis price index is calculated by using a special iterative algorithm from Chessa (2016). It measures the price dynamics by comparing period end to period start (both start and end must be inside the considered time window). To get information about both price index values and corresponding dates, please see functions: price_indices or final_index. The function does not take into account aggregating over outlets or product subgroups (to consider these types of aggregating, please use the final_index function).

References

Geary, R. G. (1958). A Note on Comparisons of Exchange Rates and Purchasing Power between Countries. Journal of the Royal Statistical Society, Series A, 121, 97-99.

Khamis, S. H. (1970). Properties and Conditions for the Existence of a new Type of Index Number. Sankhya Series B32, 81-98.

Chessa, A.G. (2016). A New Methodology for Processing Scanner Data in the Dutch CPI. Eurona 1/2016, 49-69.

Examples

gk(milk, start="2019-01", end="2019-08",window=10)
gk(milk, start="2018-12", end="2019-12")