Chapter 4 alluded to problems regarding the use of product prices in the estimation of output, problems which were not addressed in the calculation of my first published estimates. The main problem is the choice of prices, or the choice of base year prices from which to recalculate other years with the help of Thomas Barrington's product price indexes (reproduced as Table A4.6). Barrington's purpose was to produce a set of indexes which could be used in comparative price terms. The actual prices, in nominal £-s-d, were not fundamentally important so long as the trend of each product price correctly captured the true course of actual prices. The Registrar General of Ireland in the late nineteenth century, Dr Thomas Wrigley Grimshaw, presented evidence to a Royal Commission in the 1890s concerned with financial relations between Great Britain and Ireland. Amongst other things he was concerned with the estimation of the value of Irish agricultural output. He was fully aware of some of the problems of estimation which modern historians also face. His concern was with the identification of what he called ‘standard prices’. He said:

I am fully aware of the difficulties and fallacies attending attempts to estimate the value of agricultural produce from the available data as to prices. I take the prices which have been carefully collected by the Farmers Gazette and published in Purdom's Almanack as the most extensive and reliable set of standard prices available.

In my original estimates of agricultural output I used precisely those prices which Grimshaw advocated, in the form which he presented them in his evidence to the Cowper Commission published in 1887.