Most countries collect data on their imports and exports. International and regional organizations--such as the UN, OECD, and U.S. Census Bureau--then compile and publish countries' trade data for comparison.

Trade statistics sources use one or more specialized classification codes to group commodities.

Sources also vary in the currency of information and the years and countries they cover. Researchers must sometimes make trade-offs between:

• having very current information or finer levels of product detail and
• having time depth or a desired trade classification.