Since it was developed independently by  and  more than five decades ago, the gravity model has become the main econometric framework for estimating ex post the „partial“ (or direct) effects of different types of economic integration agreements on bilateral trade flows. Our estimation strategy follows that of  and . In particular, we control multilateral resistance conditions by integrating fixed effects on export time and import time.  pointed out that the gravity model theory implies that not only bilateral trade costs (bilateral trade resistance), but also trade costs relative to the rest of the world (multilateral opposition to trade) are relevant to predicting bilateral trade flows. In addition, we control endogeneity through bilateral fixed effects. This issue has received a great deal of attention in the empirical literature of the gravitational equation, as  has found that trade agreements are not exogenous. They showed that the ex post estimate of the partial effects of free trade agreements (EEAs) was warped, mainly due to the self-selection of pairs of countries in the agreements (due to the level of trade that exists), and found that this self-selection bias can be significantly reduced if some specific effects are used or when differentiated data are used. Critics of non-reciprocal preferential regimes have traditionally argued that developing countries should shift their dependence on unilateral trade preferences to reciprocal agreements, which require a stronger, credible and sustainable commitment (cf. B ;  and ).
This approach is also supported by those who believe that the argument of the children`s industry, often used to justify unilateral concessions, is a fallacious argument. 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.