In 2015, the Congressional Research Service concluded that the "net overall effect of NAFTA on the US economy appears to have been relatively modest, primarily because trade with Canada and Mexico accounts for a small percentage of US GDP. However, there were worker and firm adjustment costs as the three countries adjusted to more open trade and investment among their economies." The report also estimated that NAFTA added $80 billion to the US economy since its implementation, equivalent to a 0.5% increase in US GDP.