gk_fbmw {PriceIndices}

Extending the multilateral Geary-Khamis price index by using the FBMW method.

Description

This function returns a value of the multilateral Geary-Khamis price index extended by using the FBMW (Fixed Base Moving Window) method.

Usage

gk_fbmw(data, start, end)

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. "2019-12".

end

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

Value

This function returns a value of the multilateral Geary-Khamis price index extended by using the FBMW (Fixed Base Moving Window) method. It measures the price dynamics between periods end and start and it uses a 13-month time window with a fixed base month taken as year(end)-1. If the distance between end and start exceeds 13 months, then internal Decembers play a role of chain-linking months. The month of the start parameter must be December. 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.

Lamboray, C.(2017). The Geary Khamis index and the Lehr index: how much do they differ? Paper presented at the 15th Ottawa Group meeting, 10-12 May 2017, Elville am Rhein, Germany.

Examples

gk_fbmw(milk, start="2019-12", end="2020-04")