Nontariff barriers (NTBs) refer to the wide range of policy interventions other than border tariffs that affect trade of goods, services, and factors of production. Most taxonomies of NTBs include market-specific trade and domestic policies affecting trade in that market. Extended taxonomies include macro-economic policies affecting trade. NTBs have gained importance as tariff levels have been reduced worldwide. Common measures of NTBs include tariff-equivalents of the NTB policy or policies and count and frequency measures of NTBs. These NTB measures are subsequently used in various trade models, including gravity equations, to assess trade and/or welfare effects of the measured NTBs.
Beghin, John C., "Nontariff Barriers" (2006). CARD Working Papers. 442.