gekslm {PriceIndices}

Calculating the multilateral GEKS-LM price index

Description

This function returns a value of the multilateral GEKS-LM price index (to be more precise: the GEKS index based on the Lloyd-Moulton price index).

Usage

gekslm(data, start, end, sigma = 0.7, 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".

sigma

The elasticity of substitution (a parameter used in the Lloyd-Moulton index formula).

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 GEKS-LM price index (to be more precise: the GEKS index based on the Lloyd-Moulton price index) which considers the time window defined by wstart and window parameters. 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

Gini, C. (1931). On the Circular Test of Index Numbers. Metron 9:9, 3-24.

Elteto, O., and Koves, P. (1964). On a Problem of Index Number Computation Relating to International Comparisons. Statisztikai Szemle 42, 507-518.

Szulc, B. (1983). Linking Price Index Numbers. In: Price Level Measurement, W. E. Diewert and C. Montmarquette (eds.), 537-566.

Lloyd, P. J. (1975). Substitution Effects and Biases in Nontrue Price Indices. The American Economic Review, 65, 301-313.

Moulton, B. R. (1996). Constant Elasticity Cost-of-Living Index in Share-Relative Form. Washington DC: U. S. Bureau of Labor Statistics, mimeograph

Examples

gekslm(milk, start="2019-01", end="2019-08",window=10)
gekslm(milk, start="2018-12", end="2019-12", sigma=0.5)