Source: University of Pennsylvania
Release: Penn World Table 7.1
Exports plus Imports divided by GDP is the total trade as a percentage of GDP.
For more information and proper citation see http://www.rug.nl/research/ggdc/data/pwt/pwt-7.1
Source Indicator: openk
University of Pennsylvania, Openness at constant prices for United States [OPENRPUSA156NUPN], retrieved from FRED, Federal Reserve Bank of St. Louis; https://fred.stlouisfed.org/series/OPENRPUSA156NUPN, June 22, 2018.