48. It was clear to the Group at the very outset of its exercise that the collection of statistical data from participating countries had to take Place through an iterative process in close co-operation with the contacts. It was also seen by the Group when assessing its mandate that this collection Of data must 90 well beyond the type of information that was already being submitted by several States within the framework of the United Nations reporting system, which applies to military expenditures only. / l . . A/40/421 English Page 18 49. In this exercise, information was also needed on prices and characteristics of different military items (for example, goods and services bought by the military sector) , in addition to such military expenditure data which already had or were being submitted to the United Nations by the participating countries on a regular basis or directly to the Group in the course of its exercise, 50. The selection and collection of this additional information had to proceed in stages, taking into account a number of difficulties with regard to the availability, interpretation and comparability of the data to be submitted by participating countries. 51. All through the exercise, the matrix of the United Nations reporting instrument served as an important basis for the Group’s work on selecting and specifying its requests for data. In this matrix, military expenditures are disaggregated into operating costs, procurement and construction and research and development, and also into sub-subcategories such as purchased services and armoured vehicles, which allows for a rather detailed distribution of reporting countries 1 military expenditures among different cost categories. The Group endeavoured to obtain prices and product descriptions for a number of items within each of these sub-subcategories. The approach to obtain this objective could, however, for reasons described below not be the same for all the three major cost categories. 
**Analysis**
The text appears to be discussing the collection of data on military expenditures and the characteristics of military items, which suggests that it is related to national defense and security. The mention of the United Nations reporting system and the matrix of the United Nations reporting instrument also implies that the text is related to international cooperation and reporting. Given these hints, I hypothesize that the text is most likely related to the field of security and defense.

**Category**
Defense, International relations