Non-food production index covers non-food items. All the indices at the country, regional and world levels are calculated by the Laspeyres formula. Production quantities of each commodity are weighted by 1999-2001 average international commodity prices and summed for each year. To obtain the index, the aggregate for a given year is divided by the average aggregate for the base period 1999-2001. It should be noted that when calculating indices of agricultural, food and nonfood production, all intermediate primary inputs of agricultural origin are deducted. However, for indices of any other commodity group, only inputs originating from within the same group are deducted; thus, only seed is removed from the group “crops” and from all crop subgroups, such as cereals, oil crops, etc.; and both feed and seed originating from within the livestock sector (e.g. milk feed, hatching eggs) are removed from the group “livestock products”. For the main two livestock subgroups, namely, meat and milk, only feed originating from the respective subgroup is removed. The "international commodity prices” are used in order to avoid the use of exchange rates for obtaining continental and world aggregates, and also to improve and facilitate international comparative analysis of productivity at the national level. These” international prices”, expressed in so-called "international dollars”, are derived using a Geary-Khamis formula for the agricultural sector. This method assigns a single “price” to each commodity. For example, one metric ton of wheat has the same price regardless of the country where it was produced. The currency unit in which the prices are expressed has no influence on the indices published. The indices are calculated from production data presented on a calendar year basis. Aggregates are the sum of available data. For some item aggregates, conversion factors are applied to values when calculating totals. Please see item Metadata for the factors at FAOSTAT. The FAO indices may differ from those produced by the countries themselves because of differences in concepts of production, coverage, weights, time reference of data and methods of calculation.