15.14. The need for quantity information. Quantity is an important dimension of international trade statistics which is indispensable for various policy and analytical purposes, including for the planning of transport infrastructure, the compilation of energy, agricultural and other commodity balances, the assessment of the impact of international trade on the environment, and the verification of trade values and the construction of trade index numbers.
15.15. Challenges in the compilation of quantity data. Often quantity, whether supplementary quantity or net weight, is not provided by the traders completing the customs declarations. In other cases, the quantity provided is not correct or the supplementary quantity is provided in a quantity unit different from the one recommended for the particular commodity. For instance, when a shipment contains several different commodities, the quantity might be given as the gross weight of the shipment. Further, in commercial practice, barrels are often used instead of weight and appropriate conversion factors may not be available. Also, the customs administration is generally more interested in the quantity information for imports than in that for exports, since quantity information is, in some cases, utilized to determine both import duties and the unit values used to validate the price and value information declared by the importers.
15.16. Best practices in improving the compilation of quantity data. It is recommended that the training courses for traders on filling out customs declarations devote sufficient attention to the correct declaration of quantity information on the customs forms.
15.17. Quantity aggregations. The compilation of quantity aggregates has both an analytical and a quality dimension, owing to the heterogeneity of the goods that constitute broader commodity groups. As the proper use of quantity aggregates is limited to very specific types of analysis (e.g., of transportation issues), it is good practice to provide users with clear information on the heterogeneity underlying each quantity aggregate, and to encourage, for instance, the use of foreign trade indices as alternative measures of aggregate volume and price trends.