tpd {PriceIndices}

Calculating the multilateral TPD price index

Description

This function returns a value of the multilateral TPD (Time Product Dummy) price index.

Usage

tpd(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 TPD 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). Please note that a Weighted Least Squares (WLS) regression is run with the expenditure shares in each period serving as weights.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

de Haan, J. and F. Krsinich (2014). Time Dummy Hedonic and Quality-Adjusted Unit Value Indexes: Do They Really Differ? Paper presented at the Society for Economic Measurement Conference, 18-20 August 2014, Chicago, U.S.

Examples

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