促进pta增长的因素包括市场竞争力的扩张。第一个因素是，这些国家的目标是进入市场更大的pta。由于贸易的开放性，pta可以快速扩张。另一个因素是，那些贸易广泛且高度依赖海外贸易的国家之间存在PTA (Freund, 2000);更好的成员分配有助于扩大pta。而且，当有大量的参与者时，也会有相应的扩展。那些以统一方式确定pta成员规模的安排可能会扩大。pta的扩张也受到战略相互依赖的影响。
更深层次的安排是涉及范围更广的问题，这些问题导致与PTAs有关的过程的总体复杂性增加，以及候选人可能遵守的政策范围(Bhagwati, J.和Panagariya, 1999)。另一方面，肤浅的安排包含较少的与pta相关的问题。
Factors contributing to the growth of PTAs include the expansion because of the market competence. The very first factor is that the countries aim to enter into PTAs with the markets which are bigger. PTAs cover a large market and thus they have larger expansion, Because of the openness of the trade, PTAs can be expanded rapidly. Another factor is that a PTA is done between those countries which have extensive trade and high dependency on the overseas commerce (Freund, 2000); the better distribution of members can help in the expansion of PTAs. Also, when there are large participations, there is an expansion in the same. Those arrangements in which the members of PTAs are sized in a uniform manner may expand. The expansion of PTAs is also affected by the strategic interdependence.
Empirical analysis may be defined as the analysis in which the evidence obtained must be based on some or other kinds of evidence. This evidence may be obtained either by the scientific research or the use of working hypothesis which can be tested with the help of the observation and experimentation.
The authors have used empirical evidence in the form of observation done from the survey or an interview or on the basis of the results which has been obtained from the experiments. This includes the implementation of the scientific method which either begins with the questions or the hypothesis. On the basis of the same, the required knowledge is obtained which may either support or disapprove a specific theory.
Deeper arrangements are the ones in which the wider number of issues have been covered which lead to the increase in the overall complexity of the process related to PTAs and the range of the policies which may be adhered by the candidates (Bhagwati, J. and Panagariya, 1999). Shallow arrangements, on the other hand, consist of less number of issues related to PTAs.
The article states that there are three man indicators of depth. The very first indicator is the extent of integration which may be aimed by the preferential groups. The second indicator of depth is if the group will be able to be marked because of the formal dispute settlement mechanism. The third indicator of depth is the trade volume which may be there among the members. In one of the previous empirical works, the volume of trade has been used for the measurement of the depth with the preferential groups.
Robustness checks help in the addressing of the model by including the year specific fixed effects to the accounts for the shocks which may be felt throughout the system of globalization at any given point of time.