This information will lay the groundwork for new research in international economics and other fields. A large body of economic literature has looked at the effects of PTAs on international trade flows and on welfare.<sup>3</sup> However, this literature has two important limitations.<sup>4</sup> On the theoretical side, the study of PTAs is mostly based on Vinerian<sup>5</sup> logic, which focuses exclusively on tariffs, thus by construction excluding deep integration issues. On the empirical side, attempts to quantify the effects of PTAs suffer from a measurement error problem, as studies generally rely on dummies to identify trade agreements or distinguish between broad categories of agreements such as FTAs or CUs. The new data will help theorists to model DTAs and help empirical economists to properly identify their effects. Beyond economics, the data will inform research in other fields, primarily international law and international relations, on important issues such as the commonality or divergence of the rules set in PTAs and how they could evolve in the future.

The new data is the result of collaboration among the World Bank, the International Trade Center (ITC), the Organization for Economic Development and Cooperation (OECD), the WTO, and experts from academic institutions. It builds on previous research by the World Bank and others. A first database on the content of deep trade agreements was published in 2017 with the goal of documenting how the policy areas covered by PTAs had increased over time (Hofmann et al. 2019). This data set allowed researchers to construct a first series of indicators which capture the scope of trade agreements; i.e., what policy areas they cover. We refer to this as the _extensive margin_ of PTA depth. Based on this first data set, several research papers then looked, respectively, at the impact of deep trade agreements on trade, global value chains, foreign direct investment, and the effect of breaking up such agreements.<sup>6</sup> The data have also been extensively employed for policy advice by the World Bank in several developing countries in Africa, Latin America, East Asia and the Balkans.

The new data that we briefly review in this paper and that are analyzed in detail in the individual chapters of the Handbook offer insights into a different dimension of PTAs depth. They capture the detailed commitments to establish and preserve the rights to economic integration, and the procedures, institutions and enforcement mechanisms that countries set up to make deep integration work. The focus is therefore not on the extensive margin of integration (number of policy areas that are covered by the agreement), but on its _intensive margin_ (the specific commitments within a policy area).

While there are a number of individual studies that have documented the deepening of PTAs in specific areas, two major data collection projects—Dür et al. (2014) and Acharya (2016)—also aimed at documenting the specific commitments for a group of policy areas covered in PTAs. Both efforts have important merits. Dür et al. (2014) covered a large set of PTAs, including those that have been notified to the WTO but are no longer in force. Acharya (2016) provided a series of databases on the content of PTAs that go beyond specific policy areas and cover emerging issues such as e-commerce or the rules on dispute settlement in PTAs. Relative to these data collection projects, the new data set is more comprehensive, both in terms of the number of policy areas covered and in terms of the information on detailed disciplines in each area.

> 3 See, e.g., Freund and Ornelas 2010, Limao 2017. 4 See, e.g., Baldwin 2010, Mattoo et al. 2017. 5 Viner 1950.

> 6 Mattoo et al. 2017, Mulabdic et al. 2017, Laget et al. 2018, Laget et al. 2019.

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