relative to those for agriculture. For poorer countries, however, agriculture is a much larger share of GDP and employment, and their industrial and service sectors are often highly protected from import competition. In such cases, a cut in low levels of agricultural protection could actually worsen national economic welfare, yet such partial equilibrium models would suggest there would be an economic gain (Martin 1997, Anderson 2002a). Also, multilateral agricultural reform is not undertaken in isolation but – since the Uruguay Round at least -- as part of a package of trade reforms affecting all sectors. For these reasons, partial equilibrium global models began to be superseded from the early 1990s as CGE models became more disaggregated with the growth in capacity and speed of computers and in the quality of the needed data. Initial efforts to apply CGE models to agricultural protection issues are reported in Goldin and Knudsen (1990), but the quality of the models and applications rose dramatically over the 1990s.

# _b. Computable general equilibrium (CGE) national and global models_

The first CGE models began appearing in the 1970s, and by the early 1980s they were being used routinely for policy analysis in a number of OECD countries. For example, building on Evans (1972) pioneering work, the first detailed model build for Australia, known as ORANI (Dixon et al. 1982), produced results for a wide range of policy issues and made a major impact on policy debate during the microeconomic reform decade of the 1980s (Powell and Snape 1993; Anderson 2003b). As noted in the surveys by Shoven and Whalley (1984) and Robinson (1989), models were also beginning to be built at that time for developing countries, an early example being Dervis, de Melo and Robinson (1982). Since then many of these national models have become far more sophisticated, and in particular have added regional, occupational and household disaggregations and have become dynamic (as for example in the transforming of the Australian ORANI model into the MONASH model – see Dixon and Rimmer 2002). The latter feature a **l** ows forecasting though time and hence can show paths of adjustment to shocks – something about which politicians are especially anxious.

Global CGE models were slower in coming, since they require so much more data than national or regional models. Early examples are Whalley (1985) and Deardorff and Stern (1986, 1990), with the latter having more country and commodity detail. The Australian Government’s Industry Commission also began building a global CGE model for trade negotiating purposes (the SALTER model – see Jomini et al. 1991). A copy of that model was taken to Purdue University and, since the early 1990s, it has been improving constantly and been made publicly available as the so-called GTAP model and database (Global Trade Analysis Project – see Hertel 1997). The extraordinary efforts by Tom Hertel to train users and recruit willing helpers to revise and update the production, trade and protection data and improve the theory in the model has resulted in hundreds of people becoming persistent users and thousands of simulation experiments being published since its creation (see www.gtap.org). That openness, which has been characteristic of some other CGE modelling groups too, has been a great spur to modelling innovations.

The basic global GTAP model is similar in architecture to the Australian ORANI model, but more complex versions are being developed all the time. Among the modifications that have been incorporated for particular applications are scale economies and imperfect competition (Francois 1998), dynamics through capital accumulation (Francois and McDonald 1996), and those plus foreign direct investment (Dee, Hanslow and Phamduc 2000). In addition, computational tools for practical policy analysis have been developed to enable systematic sensitivity analysis (Pearson and Arndt 2000) and decomposition of economic welfare results (Huff and Hertel 2001). Trade and related policy analysis is now 16