temptation and social security in a dynastic framework abstract we investigate welfare and aggregate implications of a pay as you go payg social security system in a dynastic framework in which individuals have self control problems the presence of self control problems induces individuals to save less because of their urge for temptation towards current consumption individuals efforts to balance between the short term urge for temptation and the long term commitment for consumption smoothing result in self control costs in this environment payg social security works as a self control cost reducing device in contrast the presence of altruism induces individuals to save more this in turn mitigates the adverse effects of self control problems and payg social security on savings but magnifies the self control costs we find that in our environment the adverse welfare effects of a payg system are further mitigated relative to the environments that incorporate altruism and self control issues separately however the level of mitigation is quite modest

constrained efficiency in the neoclassical growth model with uninsurable idiosyncratic shocks we investigate the welfare properties of the one sector neoclassical growth model with uninsurable idiosyncratic shocks we focus on the notion of constrained efficiency used in the general equilibrium literature our characterization of constrained efficiency uses the first order condition of a constrained planner s problem this condition highlights the margins of relevance for whether capital is too high or too low the factor composition of income of the consumption poor using three calibrations commonly considered in the literature we illustrate that there can be either over or underaccumulation of capital in steady state and that the constrained optimum may or may not be consistent with a nondegenerate long run distribution of wealth for the calibration that roughly matches the income and wealth distribution the constrained inefficiency of the market outcome is rather striking it has much too low a steady state capital stock

recent trends in the size structure of italian manufacturing firms this paper analyses the re emergence of small scale production which has characterised the more recent phase of industrial development in western countries providing updated evidence about the phenomenon and focussing in particular the attention on italy where it has been assuming peculiar relevance

from global economic modelling to household level analyses of food security and sustainability how big is the gap and can we bridge it policy and decision makers have to make difficult choices to improve the food security of local people against the background of drastic global and local changes ex ante impact assessment using integrated models can help them with these decisions this review analyses the state of affairs of the multi scale modelling of policy interventions with an emphasis on applications in developing countries and livestock systems existing models do not sufficiently capture the complexity of human environment interactions across different scales and especially the link between landscape and local market levels and national and sub national level policies and markets is missing the paper suggests a step wise approach with increasing data needs to bridge this gap improvements need to be made at the description of effects of the distribution of local markets on price formation and the representation of farm diversity within a landscape analyses in contrasting agro ecological systems are needed to derive generic summary functions that can be used as input for macro level model analyses this is especially pertinent for macro level descriptions of crop and livestock production in relation to price developments and of the mosaic of different agricultural land use responses in regions with contrasting socio economic conditions and developments

taxing capital not a bad idea after all we quantitatively characterize the optimal capital and labor income tax in an overlapping generations model with idiosyncratic uninsurable income shocks and permanent productivity difierences of households the optimal capital income tax rate is signiflcantly positive at 36 percent the optimal progressive labor income tax is roughly a at tax of 23 percent with a deduction of 7 200 relative to average household income of 42 000 the high optimal capital income tax is mainly driven by the life cycle structure of the model whereas the optimal progressivity of the labor income tax is attributable to the insurance and redistribution role of the tax system jel e62 h21 h24

optimal capital income taxation with incomplete markets borrowing constraints and constant discounting for a wide class of infinitely lived agent models chamley has shown that the optimal capital income tax rate is zero in the long run lucas has argued that for the u s economy there is a significant welfare gain from switching to this policy this paper shows that for the bewley class of models with incomplete insurance markets and borrowing constraints the optimal tax rate on capital income is positive even in the long run therefore cutting the capital income tax to zero may well lead to welfare losses

optimal taxation merging micro and macro approaches efficient provision of social insurance and efficient redistributionofresourcesamongindividualsaresomeofthemostimportantandchallenging questions in macroeconomics and public finance a seminal contribution of mirrlees 1971 is the starting point for the modern approach to answering these questions a trade off between efficiency and insurance or equity is inherent to this approach and is a key determinant of the optimal policy in this paper we argue that the large body of research that follows mirrlees approach has been developing in two quite separate directions referred to in this paper as the micro and macro approaches we argue that merging the two directions

global land use implications of first and second generation biofuel targets recently an active debate has emerged around greenhouse gas emissions due to indirect land use change iluc of expanding agricultural areas dedicated to biofuel production in this paper we provide a detailed analysis of the iluc effect and further address the issues of deforestation irrigation water use and crop price increases due to expanding biofuel acreage we use globiom an economic partial equilibrium model of the global forest agriculture and biomass sectors with a bottom up representation of agricultural and forestry management practices the results indicate that second generation biofuel production fed by wood from sustainably managed existing forests would lead to a negative iluc factor meaning that overall emissions are 27 lower compared to the no biofuel scenario by 2030 the iluc factor of first generation biofuels global expansion is generally positive requiring some 25 years to be paid back by the ghg savings from the substitution of biofuels for conventional fuels second generation biofuels perform better also with respect to the other investigated criteria on the condition that they are not sourced from dedicated plantations directly competing for agricultural land if so then efficient first generation systems are preferable since no clear technology champion for all situations exists we would recommend targeting policy instruments directly at the positive and negative effects of biofuel production rather than at the production itself

policy analysis and advocacy for livestock based development the gap between household level analysis and higher level models the dichotomy in approaches to policy analysis for developing countries livestock sectors is presented substantial experience and information generated from a large number of household level studies is not being utilised by macro and aggregate models which fail to recognise heterogeneity dynamics and fundamental drivers of change in livestock systems household level studies are not standardised and rarely identify and characterise key drivers and mechanisms for exploiting heterogeneity in policy analysis the paper provides an overview of a set of six papers contained in a special edition which define and address this gap in analytical approaches and identify aspects of the way forward evidence is presented of inconsistencies and practicalities which emphasise the gap but all papers present evidence of integrative progress and list opportunities for accelerating it constraints on the subject matter are outlined and a challenge to livestock policy analysts is made

taxation and household labor supply we evaluate reforms to the u s tax system in a life cycle setup with heterogeneous married and single households and with an operative extensive margin in labor supply we restrict our model with observations on gender and skill premia labor force participation of married females across skill groups children and the structure of marital sorting we concentrate on two revenue neutral tax reforms a proportional income tax and a reform in which married individuals flle taxes separately separate flling our flndings indicate that tax reforms are accompanied by large increases in labor supply that difier across demographic groups with the bulk of the increase coming from married females under a proportional income tax reform married females account for more than 50 of the changes in hours across steady states while under separate flling reform married females account for all the change in hours

the surprising power of age dependent taxes this paper provides a new empirically driven application of the dynamic mirrleesian framework by studying a feasible and potentially powerful tax reform age dependent labour income taxation i show analytically how age dependence improves policy on both the intratemporal and intertemporal margins i use detailed numerical simulations calibrated with data from the u s panel study of income dynamics to generate robust policy implications age dependence 1 lowers marginal taxes on average and especially on high income young workers and 2 lowers average taxes on all young workers relative to older workers when private saving and borrowing are restricted finally i calculate and characterize the welfare gains from age dependence despite its simplicity age dependence generates a welfare gain equal to between 0 6 and 1 5 of aggregate annual consumption and it captures more than 60 of the gain from reform to the dynamic optimal policy the gains are due to substantial increases in both efficiency and equity when age dependence is restricted to be pareto improving the welfare gain is nearly as large

measurement of competitiveness in smallholder livestock systems and emerging policy advocacy an application to botswana farm level cross sectional data of 556 randomly selected livestock producers were used to investigate the competitiveness of smallholder beef farmers in botswana the results show the presence of inefficiency with about 74 of the variation in actual profit from maximum profit profit frontier between farms mainly arising from differences in farmers practices rather than random variability further the mean profit efficiency level of 0 58 suggests that there is a substantial scope to improve beef profitability in botswana significant profit efficiency drivers include among others education distance to market herd size access to information and access to income from crop production considering the importance of livestock sector for wealth creation and poverty eradication in the rural areas where poverty is more pronounced there is a need for appropriate development strategies and policies directed towards addressing these factors in particular there is need to invest in market infrastructure in order to improve market access hence profit efficiency of smallholder livestock farmers

insurance and taxation over the life cycle we consider a dynamic mirrlees economy in a life cycle context and study the optimal insurance arrangement individual productivity evolves as a markov process and is private information we use a first order approach in discrete and continuous time and obtain novel theoretical and numerical results our main contribution is a formula describing the dynamics for the labour income tax rate when productivity is an ar 1 our formula resembles an ar 1 with a trend where i the auto regressive coefficient equals that of productivity ii the trend term equals the covariance productivity with consumption growth divided by the frisch elasticity of labour and iii the innovations in the tax rate are the negative of consumption growth the last property implies a form of short run regressivity our simulations illustrate these results and deliver some novel insights the average labour tax rises from 0 to 37 over 40 years whereas the average tax on savings falls from 12 to 0 at retirement we compare the second best solution to simple history independent tax systems calibrated to mimic these average tax rates we find that age dependent taxes capture a sizable fraction of the welfare gains in this way our theoretical results provide insights into simple tax systems copyright 2013 oxford university press

a quantitative analysis of capital income taxation this paper studies the quantitative impact of eliminating capital income taxation on capital accumulation and steady state welfare in a general equilibrium model with overlapping generations of sixty five period lived individuals who face idiosyncratic earnings risk borrowing constraints and life span uncertainty under a wide range of parameter configurations the capital income tax rate that maximizes steady state welfare is positive even though eliminating it completely would raise the steady state capital stock toward the golden rule this is because the tax burden is shifted toward the younger and liquidity constrained years reducing the individuals ability to self insure copyright 1998 by economics department of the university of pennsylvania and the osaka university institute of social and economic research association

the cyclical and secular behaviour of the labour input comparing efficiency units and hours worked summary a monthly labour input series designed to correct for the fact that all hours worked are not of the same quality is constructed and its properties compared with unadjusted hours worked this efficiency units series is constructed from bls data on hours worked and earnings by age and sex the cyclical fluctuations displayed by the efficiency units series are smaller on average than those displayed by hours worked although the difference is not large however the secular behaviour of the series is quite different hours worked per capita displays a significant positive trend while efficiency units per capita does not

what has been learned about labor supply in the past twenty years the main advance in the study of labor supply in the past 20 years has come in recognizing and interpreting the variety of different labor supply functions that coexist in the empirical literature a crucial theoretical distinction with important empirical payoff is that between labor supply choices at the extensive margin i e labor force participation and employment choices and choices at the intensive margin i e choices about hours of work or weeks of work for workers another important distinction is the one between a descriptive labor supply function and a structural supply function that can be the basis for out of sample policy investigations concerning responses to tax and welfare programs and evaluations of welfare losses a full understanding of the participation hours dichotomy leads to an appreciation of the importance of the problem of selection bias what is the wage to impute to a nonworking person these distinctions are a legacy of the research conducted on labor supply over the past 20 years many important empirical questions have been addressed i how strong are the effects of taxes welfare and transfer programs on labor supply ii how important is intertemporal substitution can life cycle labor supply models explain business cycle labor supply behavior iii has the consensus view of the 1960 s of high labor supply elasticities for married women and low labor supply elasticities for married men held up all of the empirical evidence assembled on labor supply must be called into question in the light of important research on the basic quality of the data conducted by analysts at the university of michigan i discuss this evidence in a concluding section except for my discussion of measurement issues i focus only on the major discoveries about which a general consensus has emerged

redistributive taxation in a simple perfect foresight model abstract we investigate the redistributive potential of capital taxation in an intertemporal maximizing model of capital formation first even unanticipated redistributive capital taxation is severely limited in its effectiveness since it depresses wages second under any convergent redistributive tax policy which maximizes a paretian social objective the capital income tax will converge to zero independent of the factor supply elasticities these results are independent of workers holdings of capital

the budgetary and welfare effects of tax deferred retirement saving accounts abstract the present paper analyzes the budgetary macroeconomic and welfare effects of tax deferred retirement saving accounts similar to u s 401 k plans in a dynamic general equilibrium overlapping generations economy with heterogeneous households because of the initial deferral of tax payments the short run budgetary cost of tax deferred accounts is significantly higher than the long run cost therefore the budget neutral introduction of tax deferred accounts would make current and near future households worse off although it would increase national wealth and total output in the long run if the government spread the short run cost to future households by increasing debt the policy change could make all age cohorts on average as well off as the economy without tax deferred accounts due to increased government debt and debt service costs however national wealth and total output would decrease in the long run thus introducing tax deferred accounts would not increase national wealth and improve social welfare at the same time this is partly because the policy change is regressive and reduces the risk sharing effect of the current income tax system

firm size and job quality a survey of the evidence from germany small firms provide and create a large proportion of jobs in germany are these jobs worse than jobs in larger firms the mosaic picture that emerges from a review of several recent empirical studies using german individual or firm level micro data shows that all in all wages are lower non wage incomes fringes are lower job security is lower work organisation is less rigid institutionalized possibilities for workers participation in decision making are weaker and opportunities for skill enhancement are worse in small firms compared to large firms the weight of evidence therefore indicates that on average small firms offer worse jobs than large firms it is argued that there is no need for policy measures targeted to improve job quality in small firms because higher incomes in large firms can in part be seen as compensating differentials for more rigid work organisation and can follow from wage policies to reduce shirking and turnover that is more costly in large than in small firms furthermore a lower level of remuneration less protection against dismissals a lower level of workers participation and less opportunities for further training all contribute to lower costs in small firms that might be needed to compensate for size related cost disadvantages compared to large firms economic policy should concentrate on keeping barriers to entrepreneurs entry to markets low to foster new firm formation and creative destruction

the choice of the personal income tax base abstract starting with vickrey 1945 and mirrlees 1971 the optimal tax literature has studied the design of a personal income tax the assumed ideal would be to tax earnings ability earnings ability is unobservable for tax purposes however past papers have focused instead on designing a tax on labor income existing tax bases though depend on a broader range of information about each individual than just labor income in principle this supplementary information can help in designing a tax that has more attractive distributional properties by more closely approximating an ability tax the objective of this paper is to lay out theoretically and estimate empirically how to make best use of available information about each individual in addition to earnings in a setting where the first best tax would be an ability tax the theory lays out an equity efficiency trade off when choosing the tax base in the empirical work we find the tax base that is best on equity grounds alone we find that the choice to tax couples based on their joint income and the inclusion of dividends interest income and dependents deduction in the tax base in roughly their current form can be rationalized simply based on their value in better approximating an ability tax without any need for supplementary motivations for these provisions however the inclusion of mortgage and property tax payments in the list of itemized deductions cannot be defended on these grounds

on the optimality of age dependent taxes and the progressive u s tax system abstract in life cycle economies where an individual s optimal consumption work plan is almost never constant the optimal marginal tax rates on capital and labor income vary with age conversely the progressivity imbedded in the u s tax code implies that marginal tax rates vary with age because tax rates vary with earnings and earnings vary with age using numerical simulations this paper shows that if the tax authority is prevented from conditioning tax rates on age some degree of progressivity is desirable as progressive taxation better imitates optimal age dependent taxes than an optimal age independent tax system this role for progressive taxation emanates from efficiency reasons and does not rely on any insurance nor re distribution arguments

integrating livestock feeds and production systems into agricultural multi market models the example of impact the various ways in which livestock production systems can be incorporated into economic partial equilibrium multi market models are presented and the challenges outlined a particular focus and illustrative case is livestock feed foremost among the challenges is the reconciliation of scientific understanding of livestock feed requirements and production characteristics with the available national data another challenge is in estimating herd structures an economic multi market modeling approach is presented which has been widely used in policy analysis and advocacy and an account is given of the necessary recent enhancements for addressing livestock

flat tax reform a quantitative exploration abstract this paper explores quantitatively the general equilibrium implications of a revenue neutral tax reform in which the current income and capital income tax structure in the u s is replaced by a flat tax as proposed by hall and rabushka 1995 the flat tax 2nd ed hoover the central aspects of such reform the impact of tax reform on capital accumulation and labor supply as well as its distributional consequences are analyzed in a dynamic general equilibrium model main results are that i the elimination of the actual taxation of capital income has an important and positive effect on capital accumulation ii mean labor hours are relatively constant across tax systems but aggregate labor in efficiency units increases iii in all circumstances analyzed the distributions of earnings income and especially wealth become more concentrated

optimal taxation in a life cycle model we extend deaton s atemporal optimal commodity tax model to a life cycle envi ronment in which the individual may choose to work in many periods we are able to con firm the corlett hague intuition goods that are more complementary with leisure should be taxed at higher rates in addition we prove that in the microeconomic framework under lying some popular general equilibrium models if real wage and interest rates are constant over the life cycle the addition of some interest taxation to a consumption tax regime would be welfare improving and that optimal labour tax rates decline with age

optimal indirect and capital taxation we consider an environment in which agents skills are private information and follow arbitrary stochastic processes we prove that it is typically pareto optimal for an individual s marginal benefit of investing in capital to exceed his marginal cost of doing so this wedge is consistent with a positive tax on capital income we also prove that it is pareto optimal for the marginal rate of substitution between any two consumption goods to equal the marginal rate of transformation this lack of a wedge is consistent with uniform taxation of consumption goods within a period

how pastoralists perceive and respond to market opportunities the case of the horn of africa this article examines how pastoralists of the horn of africa negotiate the need for herd mobility production under conditions of variable rainfall and grazing conditions with the necessity to market animals at fixed market locations it addresses a set of related questions 1 are herder mobility and other production decisions being altered by improved market opportunities 2 what roles do markets play in pastoralist drought and drought recovery strategies 3 which groups of producers are taking advantage of and or benefiting from which market chains and 4 what factors other than price help to explain why and when pastoralists sell livestock the article concludes that macro economic forecasts about supply response in the region may be overly optimistic and off target because they fail to appreciate the non price factors that influence pastoralist households decisions to sell livestock

an analysis of fiscal policy with endogenous investment specific technological change the effects of distortional fiscal policies are studied within a model in which there is endogenous investment specific technological change labor is used in the production of output and also for research purposes labor or capital taxes then distort the trade off between developing new technologies and investing in existing types of capital it is shown that if there is an externality in the research activity then it may be socially optimal to impose both a capital tax and an investment tax credit the growth rate is shown to be increasing in the rate of capital taxation and decreasing in the rate of labor taxation although the effect of taxation on the growth rate is modest this supports the observation that there is relatively little relationship between growth rates of economies and their rates of taxation

labor dependent capital income taxation abstract capital taxation which is negatively correlated with labor supply is proposed this paper uses a life cycle model of heterogeneous agents that face idiosyncratic productivity shocks and shows that the tax scheme provides a strong work incentive when households possess large assets and high productivity later in the life cycle when they otherwise would work less the system also adds to the saving motive of prime age households and raises aggregate capital the increased economic activities expand the tax base and the revenue neutral reform results in a lower average tax rate the negative cross dependence generates a sizable welfare gain in the long run relative to the tax system that treats labor and capital income separately as a tax base the reform however can hurt the elderly during the transition with a high marginal tax on their capital income

on income and wealth taxation in a life cycle model with extensive labour supply in a stationary life cycle model with extensive labour supply two forms of taxation are studied non linear income taxation and linear wealth taxation in the life cycle model the social weights of the dynasties depend on their permanent incomes not on the observed taxable current income a tax on wealth then can complement income tax as a redistributive tool the derivative of social welfare with respect to the wealth tax rate at the no tax point is computed it is positive whenever permanent income is positively correlated with aggregate life time savings this result is illustrated on a numerical example

the pattern of changes in the long term development of establishment size hypotheses and analyses dealing with the expansion of small businesses are usually carried out over relatively short periods of time the patterns drawn from these examinations e g on the question of specific differences in the growth of size are usually influenced by configurations of the overall economy and limit the realization of regular processes to the phases they are based upon a second disadvantage lies in most cases in the fact that data sources are used for the empirical analyses that do not cover the economic system as a whole nor for all sizes of establishments this study attempts to present the development of the sizes of establishments in germany over a period of more than one hundred years 1882 to 1987 and thus avoids the narrow perspective of previous examinations it becomes evident that this development does not take a continuous course instead it follows a wave pattern since this discontinuous development pattern is common to almost all sectors it appears to be a general phenomenon this study reveals that the small establishments with more than five employees contrary to most theoretical assumptions are of utmost importance even when considered over a long period of time the growth of small establishments in recent years observable in all sectors may not be a unique phenomenon however in view of an overall growth of employment and the simultaneous shrinking of large establishments it occurs under a new constellation

financing the german mittelstand this paper describes how the german mittelstand or small and medium sized enterprises are financed in germany the role of the german mittelstand both in a static and in a dynamic framework is described and contrasted with that of the same size group in other leading industrialised countries we find that in general the mittelstand has played a mmore important role in germany than in other industrialised nations such as the united states or the united kingdom the traditional success of the german mittelstand is partly attributable to a system of finance that is richly layered by complementary institutions designed to meet the financial needs of both large and smaller enterprises however we find evidence that even under the german system of finance liquidity constraints exist and are greater for smaller firms the german system of finance moreover seems particularly deficient in the channeling of funds to new firm startups in the newer industries

consumption taxes and economic efficiency with idiosyncratic wage shocks fundamental tax reform is examined in an overlapping generations model in which heterogeneous agents face idiosyncratic wage shocks and longevity uncertainty a progressive income tax is replaced with a flat consumption tax if idiosyncratic wage shocks are insurable i e no risk this reform improves interim efficiency a result consistent with the previous literature but if more realistically wage shocks are uninsurable this reform reduces efficiency even though national wealth and output increase over the entire transition path this efficiency loss in large part stems from reduced intragenerational risk sharing that was previously provided by the progressive tax system

optimal life cycle unemployment insurance we argue that us welfare would rise if unemployment insurance were to be increased for young workers and decreased for old this is because young workers have little means to smooth consumption during unemployment and want jobs to accumulate high return human capital so unemployment insurance is highly valuable to them while the induced moral hazard problem is mild we consider a life cycle model with unemployment risk and endogenous search eort that we calibrate to match us labor market institutions we nd that allowing unemployment replacement rates and other government transfers to decline with age yields sizeable welfare gains which amount to around two thirds of the gains attained under the constrained optimal scheme for unemployment insurance over the life cycle

age dependent employment protection this paper examines the age related design of firing taxes by extending the theory of job creation and job destruction to account for a finite working life time we first argue that the potential employment gains related to employment protection are high for older workers as they are magnified by the proximity to retirement but higher firing taxes for these workers increase job destruction rates for the younger generations furthermore from a normative standpoint when firms cannot ex ante age direct their search the impact of each generation of unemployed workers on the average return on vacancies makes the internalization of the search costs for the other generations imperfect through the ex post nash bargaining process we show that the first best age profile of firing taxes is typically hump shaped partially in contradiction with existing policies in some european countries taking into account the fact that the human capital of older workers is more specific than general tends to exacerbate these results

the timing of redistribution we investigate whether late redistribution programs that can be targeted toward low income families but that may distort savings decisions can dominate early redistribution programs that cannot be targeted as a result of information constraints we use simple two period overlapping generations models with heterogeneous agents under six policy regimes a model calibrated to the u s economy benchmark two early redistribution lump sum regimes two targeted late redistribution regimes and finally a model without taxes and redistribution redistribution programs are financed by a labor tax on the young generation and a capital tax on the old generation we argue that if the programs are small in size late redistribution can dominate early redistribution in terms of welfare but not in terms of real output better targeting of low income households cannot completely offset savings distortions in addition we find that the optimal transfer and tax policy implies a capital tax of 100 and transfers exclusively to the young generation

simulating fundamental tax reform in the united states this paper uses a new large scale dynamic life cycle simulation model to compare the welfare and macroeconomic effects of transitions to five fundamental alternatives to the u s federal income tax including a proportional consumption tax and a flat tax the model incorporates intragenerational heterogeneity and a detailed specification of alternative tax systems simulation results project significant long run increases in output for some reforms for other reforms namely those that seek to insulate the poor and initial older generations from adverse welfare changes long run output gains are modest

the impact of biofuel growth on agriculture why is the range of estimates so wide the rapid expansion of biofuel production has generated considerable interest within the body of empirical economic literature that has sought to understand the impact of biofuel growth on the global food economy while the consensus within the literature is that biofuel emergence is likely to have some effect on future world agricultural market there is a considerable range in the estimated size of the impact despite the importance of this topic to policy makers there has been no study that has tried to reconcile the differences among various outlook studies this paper undertakes an in depth review of some key outlook studies which quantify the impacts of biofuels on agricultural commodities and which are based on either general equilibrium ge or partial equilibrium pe modeling approaches we attempt to reconcile the systematic differences in the estimated impacts of biofuel production growth on the prospective prices and production of three major feedstock commodities maize sugar cane and oilseeds across these studies despite the fact that all models predict positive impacts on prices and production there are large differences among the studies our findings point to a number of key assumptions and structural differences that seem to jointly drive the variations we observe across these studies the differences among the pe models are mainly due to differences in the design of scenarios the presence or absence of biofuel trade and the structural way in which agricultural and energy market linkages are modeled the differences among the ge models are likely to be driven by model assumptions on agricultural land supply the inclusion of the byproducts and assumptions on crude oil prices and the elasticity of substitution between petroleum and biofuels