The next natural step is to divide the «Dummy PTA» taking into account the group to which each business partner belongs (Column 4). The results indicate that preferential trade agreements have a positive impact in all four cases. The most significant effect is trade flows between industrialized countries (0.3984), while point estimates for the other three combinations range from 0.111 to 0.248. Between 1934 and 1947, the United States entered into separate trade agreements with 29 foreign countries. The Customs Commission found that U.S. tariffs were reduced from an average of 48% to 25% on average over the 13-year period when it used duty-subject imports in 1939 as a basis for comparison.  Analyze the discrepancies between PPML and OLS estimates by Monte Carlo simulations. They indicate that PPML uses deviations from trade flows relative to their forecasts, while the OLS contains protocol deviations. They show that PPML tends to place more emphasis on couples of countries with large commercial volumes, which has an impact on results. That is why, according to Mayer et al. (2018), in the other columns of Table 3 PPML, we export export shares (bilateral exports divided by total exports) and not to export flows. That is, we appreciate Eq (3) with PPML: (3) All of the agreements mentioned above are free trade agreements, but for various reasons, members prefer to name them under another name.
In many cases, these names reflect the broader scope of agreements: many recent free trade agreements go beyond the scope of traditional trade agreements and cover areas such as public procurement, competition, intellectual property, sustainable development, labour and the environment, etc. In addition, other recent studies focus on studying the impact of non-reciprocal trade agreements on bilateral trade, including controls on regional trade agreements.  analyze the GSP with annual data for 184 countries during the period 1953-2006 and find that the GSP tends to promote exports in both directions in the short term, but hinders them in the long term. On the other hand, and , data for 1967 countries over the period 1960-2008 provide an in-depth analysis of the issue to demonstrate that NNAs have a positive influence on developing countries` exports to developed countries, but that they also have a positive effect in the opposite direction, from benefactors to recipient countries.