By NAICS

The NAICS imports and exports items are classified by output industry, not input industry. As an example, NAICS import index 326 (plastics and rubber products manufacturing) include outputs such as manufactured plastic rather than inputs such as petroleum. The NAICS classification structure also matches the classification system used by the PPI (Producer Price Index) to produce the NAICS primary products indexes.

Series IDs in FRED maintain the NAICS numbering codes system. To see the hierarchy of codes, visit http://www.census.gov/cgi-bin/sssd/naics/naicsrch?chart=2007.
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