As noted above, Table 1 reports standard errors grouped only at the pair level.  examines in a recent paper the consequences of non-compliance with the interdependence of disturbances in several dimensions, with model models for the structural gravity of cross-sectional data and bilateral trade panels, if concluded. These authors conclude that ignoring multi-channel clusters leads to misleading conclusions about the relevance of preferential trade agreements of different types, since multi-tiered consolidation has a significant impact on standard errors in commercial cost variables. To address this problem, Table 2 presents the results of multi-level grouping that allow for a correlation in the notion of error in all possible cluster dimensions. The grouping clearly has no impact on point estimates. The results show that despite significant differences between the two types of standard errors (grouped standard errors are higher), all estimates of positives at the 1% meaning level remain statistically significant and all previous conclusions remain unchanged. President Franklin D. Roosevelt signed the Reciprocal Trade Agreements Act (RTAA) in 1934. It gave the president the power to negotiate bilateral and reciprocal trade agreements with other countries and allowed Roosevelt to liberalize U.S. trade policy around the world.
It is generally attributed that it sounded the era of liberal trade policy that continued during the 20th century.  In negotiating agreements under the RTAA, the United States has generally made direct concessions only to so-called primary suppliers, namely countries that were or are likely to become the main source or important source of supply for the product in question. The concessions were granted in exchange for opening foreign markets to U.S. exports. Between 1934 and 1945, the United States signed 32 reciprocal trade agreements with 27 countries.  In addition, the conclusion of the General Agreement on Tariffs and Trade was taken by the Authority under the RTAA. During the last “Uruguay Round” (1986-1994), GATT created its own successor, the World Trade Organization (WTO), which established the basic rules for replacing bilateral agreements with a multilateral trading system between more than 140 member states. The WTO has gone beyond tariff reduction efforts to promote trade liberalization in areas such as information technology and financial services.
The WTO secretariat is based in Geneva, but decisions are taken by member states at semi-annual ministerial conferences. Because of the benefits of accession, even former communist countries, including Russia and China, have tried to join. In addition, in agreement with other recent work, we go further than  because we also take into account heteroscid residues and zero trading flows, estimating the gravitational equation in layers and not in protocols with the Fish Pseudo-Maxi Likelihood (PPML) estimate. This estimate has been made popular by  to deal with a potential heteroskedasticity distortion resulting from the linearization of gravitational equations, but it is also useful in its ability to process zeroes in bilateral trade flows. After , a large number of recent studies address the two econometric problems of PPML (see z.B, , , , , , ). However, the large datasets used in most of these studies or the difficulties encountered in achieving convergence have excluded estimating Fish`s gravity equations, including the three types of high-dimensional solid effects that must take into account both unsuserated bilateral heterogeneity and notions of multilateral resistance (country-fixing effects) , fixed effects of exporter and import time). Fortunately,  have recently implemented an iterative estimate of PPML that allows researchers to manage both problems simultaneously for both problems in a large data set, as used in c