Price indices of imports and exports illustrate the process of changing prices of industrial products in international trade. Such industrial products are covered in the sections of the Polish Classification of Goods and Services (PKWiU), such as: Mining and quarrying; Manufactured products; Electricity, gas, steam and hot water.

Price indices are developed on the basis of monthly price surveys for the selected representative goods (each month about 12 thous. of goods in exports and about 13 thous. in imports, estimation of 12 months of 2023 year), which are obtained from intentionally chosen trade operators employing 10 or more employees (about 6800 operators in total, of which about 3300 importers and about 3500 exporters).
The object of the study are prices – on the import side on a CIF basis and on the export side on a FOB basis - satisfying the conditions:
- an actual transaction price (not a price from a price list),
- prices determined on the purchase-sale invoices,
- either the price of a representative transaction (relating to a particular day of the month), or the average price of a few comparable transactions concluded during the reporting month,
- prices expressed in PLN.
The basic import/export price indices for a particular representative of goods, calculated on the basis of data obtained from the trade operators is the monthly indice calculated on the previous month base = 100. Then, price indices on the CN-8 digit level are calculated at a country-wide scale. They are calculated as geometrical averages of elementary price indices of representatives belonging to a given CN-8 digit level. Afterwards, monthly price indices calculated on the previous month base = 100 for the CN-8 digit CN level are aggregated (according to the key links between CN and PKWiU Nomenclatures) at 4-digit PKWiU level. For calculation the Laspeyres' formula is applied, ie as a weighted averages of price indices, using appropriate weighting systems. They are subsequently used, by applying weighting systems, for calculation of the higher level of PKWiU aggregation. Price indices on other basis are calculated as the average of price indices of aggregates at lower levels, weighted by the value of imports / exports. The weighting system was created on the basis of the value of imports and exports of 2021 year for price indices beginning as from 2024 year.