در ایجاد ارتباط بین شبیه سازی میکرو و مدل های تعادل عمومی قابل محاسبه با استفاده از تجمیع دقیق ناهمگن عوامل تولید گسسته - انتخاب
|کد مقاله||سال انتشار||مقاله انگلیسی||ترجمه فارسی||تعداد کلمات|
|28830||2009||11 صفحه PDF||سفارش دهید||محاسبه نشده|
Publisher : Elsevier - Science Direct (الزویر - ساینس دایرکت)
Journal : Economic Modelling, Volume 26, Issue 3, May 2009, Pages 560–570
Our paper contributes by bridging the gap between the (partial equilibrium) microsimulation and the computable general equilibrium (CGE) approaches, by making use of exact aggregation results from the discrete choice literature: heterogeneous individuals choosing within a set of discrete alternatives may be aggregated into a representative agent with (possibly multiple-level) constant elasticity-of-substitution/transformation preferences/technologies. These results therefore provide a natural link between the two policy evaluation approaches. We illustrate the usefulness of these results by evaluating potential effects of population ageing on the dynamics of income distribution and inequalities, using a simple overlapping generations model where individuals make leisure/work decisions, and choose a profession among a discrete set of alternatives.
During the last twenty years, computable general equilibrium (CGE) models have become standard tools of quantitative policy assessment. Their appeal has built on their rigorous grounding in economic theory: agents' decision-making behaviour is derived from explicit optimisation under strictly specified technological or budget constraints, given market signals that ensure global consistency. These theoretical foundations have made CGE models appear particularly useful for ex-ante evaluations of policy reforms. However, the whole apparatus relies on the concept of “representative agent” despite unclear aggregation procedures to link these aggregate optimising decision-makers to the numerous individual agents whose behaviour they are meant to capture. During the same period, another class of models has become increasingly popular: behavioural microsimulation models. Their appeal stems from the fact that they avoid any reliance on typical agents by fully taking into account the heterogeneity of individual choices as they are revealed in micro-data sets. 1 Indeed, working with myriads of actual economic agents rather than with a few hypothetical ones makes it possible to precisely identify the winners and the losers of a reform – obviously a major concern to policy-makers – yet, making it possible by simple addition to accurately measure this impact on aggregate variables. The increasing availability of large and detailed data sets on individuals makes this quite appealing. The drawback of the approach is that it is partial equilibrium in essence: for instance, individual's labour supply adjustment to some new tax incentive scheme can be quite accurately captured for given wages and other policy parameters, but market equilibrium and government budget constraints can be expected to have a feedback influence on the same individual's choices that is typically neglected. One could of course imagine iterating between the microsimulation and the CGE models, and indeed, a few efforts have successfully been done in this direction: see for instance Savard (2003) and the elaboration of Arntz et al. (2008) on Arntz et al. (2006). Though this iterative strategy might be satisfactory for some problems – in particular when dynamics are thought unimportant – it becomes tedious for more sophisticated apparatus such as overlapping generations (OLG) models: see however Rausch and Rutherford (2007) for progress in that direction. In this paper, we make use of simple yet powerful exact aggregation results due to Anderson, de Palma and Thisse (1992) (here after: AdPT) who show that, under reasonably mild conditions, heterogeneous individuals that have to choose (possibly continuous amounts) within a set of discrete alternatives may be aggregated into a representative agent with constant elasticity-of-substitution (CES) preferences.2 We illustrate how these results can be useful to CGE modellers by making available to them a growing body of empirical estimates from microeconometrics that can be used to parameterise CES/CET (constant elasticity-of-transformation) preferences/technologies in the representative agent framework. Furthermore, we argue that these results provide a natural and appealing link between the standard CGE apparatus and the microsimulations approach, and suggest that they constitute a useful alternative approach to the iterative strategy between microsimulation and CGE models. There is no free lunch, unfortunately: some details captured by the microsimulation approach could be lost, a cost that one should balance against the benefits of accounting for the general equilibrium feedbacks. We show how to make use of these results in order to link the micro and the macro simulation approaches, and illustrate the usefulness of the methodology in the context of population ageing using a calibrated overlapping generations (OLG) model. For this, we first generate in vitro a micro-data set where individuals, classified in different cells according to their socio-economic characteristics, face random utility maximisation problems over sets of discrete alternatives. We focus, for illustrative purposes, on labour market participation, and particularise the discrete choices as “to work or not to work, and if work is chosen, in which profession?” in a nested multinomial logit framework. 3 We then show that the aggregation of individual choices yields a labour-supply scheme that coincides with the one derived from a macro-agent's time-allocation problem subject to smooth nested CES preferences as typically used in CGE models. The representative agent is part of a dynamic GE model which we simulate to evaluate the effects of a demographic shock on the time path of wages and interest rates. These equilibrium prices are then plugged into the microsimulation model in order to determine the response of each individual micro-agent to the changes in his/her economic environment. From this individual choice response, we can compute the income distributions consistent with general equilibrium wages, and therefore apprehend the dynamics of income inequalities induced by population ageing. The paper is organised as follows: in Section 2, we provide a refresher on probabilistic discrete choice models. Focusing on a typical labour force participation decision problem, we show in Section 3 how to link the myriads of heterogeneous micro-agents of the microsimulation approach to a macro-agent. This macro-agent is embedded in the dynamic GE model sketched in Section 4. We then submit in Section 5 the OLG economy to an ageing shock, and plug the equilibrium prices in the microsimulation model to generate the time-path of income inequality indicators. The paper closes with a brief conclusion.
نتیجه گیری انگلیسی
Computable general equilibrium models have become indispensable tools of quantitative policy assessment. They inevitably rely on some form of representative agents simplification of the economy necessary to make explicit and manageable the consistency imposed on individual decisions by technological and resource constraints. As such, they are unable to keep track of individual heterogeneities that affect decisions at the underlying micro level. As huge micro-data sets have increasingly been made available in recent years, the microsimulation approach has gained popularity precisely because it takes into account the full heterogeneity of individual adjustments to policy reforms. In these models, individual decision is often made over a set of discrete alternatives. But this is typically a partial equilibrium approach that sacrifices global consistency. Iterations between the two frameworks is always possible, but bound to be at best tedious, possibly inaccurate or unreliable if the convergence path is ill behaved. We have suggested in this paper a bridge between the two model types by making use of some exact aggregation results that provide an interface between the two approaches. Many reasons can be mentioned that advocate for the usefulness of these aggregation results. First, it is likely that working with a well behaved aggregate agent is conceptually much easier and convenient to many modellers, when analysing GE policy results, than thinking in terms of random utility discrete choices of myriads of micro-agents. Second, the theoretical characterisation of the properties of a general equilibrium (such as existence and uniqueness of a solution, or the convergence properties of a fixed-point algorithm) is likely to be much easier if one can rely on well behaved preferences of macro-agents rather than deal with huge numbers of heterogeneous dichotomous choice-making micro-agents. Third, by avoiding the drawbacks mentioned above of an iterative procedure between the two frameworks, they make computations more accurate. The aggregation results can also prove useful to CGE modellers not interested in the articulation between their and the behavioural microsimulation approach. Indeed, the explosion of the microeconometric literature during the last two decades provides us with empirical estimates drawn from huge data sets of individual data, a large fraction of which uses some form of the nested logit model. Making use of this econometric information on preferences and/or technologies can only improve the quality of the GE predictions. We have shown how CGE modellers can easily take advantage of such empirical information with little methodological cost. Potential applications of the aggregation methodology introduced in this paper are numerous. Income inequality issues is one, as was illustrated in a dynamic setting, by linking a microsimulation model built from a computer-generated data set to a calibrated OLG general equilibrium representation of an economy submitted to demographic ageing.