text: the use of specific methods based on price’ indexes and PPPs of purchasing power of currencies, which have already been applied extensively to economic aggregates. A price index is an instrument for measuring price changes which makes it possible to express expenditures of successive time periods in terms of constant prices, namely , real expenditures. PPPs are instruments for comparing real expenditures among countries. They are a particular form of price index because they are calculated by comparing the prices of the same commodities in two or more countries at a particular point in time. Price indexes could be combined with PPPs to enable international comparisons at other points in time. B. Construction of price indexes 26. Three main methods of calculating indexes are currently used: the Laspeyres index, which uses the quantities produced or consumed in the past as weighting factors, the Paasche index, which uses the quantities of the current or latest year and lastly, the Fisher index, which is defined as the geometric mean of the two preceding indexes. Assumptions which would be made concerning a technological evolution of selected products point at the use of a chain index whereby the prices of year one are compared with those of year zero according to the weights of year one and the prices of year two with those of year one according to the weights of year two. This method is, however, not essential for the calculation of price indexes concerning a very limited number of years, as is currently being done by this Group of Experts. The Group has therefore decided to use a simple Paasche index which seemed slightly preferable to the use of a Laspeyres formula. 27. The construction of a military price index is neither a priori more difficult nor are the resu’lts less reliable than is the case for civilian price indexes, 
analysis: The text discusses the construction of price indexes and purchasing power parities (PPPs), which are economic concepts used to measure inflation and compare the purchasing power of different currencies. The text also mentions the use of specific methods and formulas to calculate these indexes, such as the Laspeyres and Paasche indexes. This suggests that the text is related to economic concepts and statistical analysis, which are typically used in the field of economics.