1. Hans Lofgren DECPG, World Bank
Introduction to MAMS – A CGE Model for Developing Country Strategy Analysis
Hans Lofgren DECPG, World Bank
Presentation for the LCSPE and DECPG training workshop “CGE Modeling for Policy Analysis,” held at the World Bank, Washington, D.C., May 28, 2013

2. Outline Introduction Model Design Model Structure The MAMS Database
User-Friendly Interface
Applications: Policy Issues and Insights
Yemen Application
References

3. Introduction MAMS = Maquette for MDG Simulations
Developed at the World Bank, initially for country-level MDG strategies
how should government and aid policies be designed to achieve the MDGs (poverty, education, health, water-sanitation)?
Evolved into a more general framework for country-level, ex-ante, medium-to-long-run development policy analysis.

4. Introduction
The main originality of MAMS is the inclusion of (MDG- and/or education-related) human development (HD) services and their impact on MDGs and other aspects of social and economic performance.
In addition:
endogenous links between education and the labor market.
disaggregation of the government spending by function into current and investment; coverage of government capital stocks
HD services may be produced by the government and the private sector.

5. Introduction
As of May 2013, MAMS applications to around 50 countries –
Two main settings:
World Bank country analysis (including Country Economic Memoranda, Public Expenditure Reviews, Poverty Assessments);
UN projects (UN-DESA + UNDP + World Bank + developing country researchers).

6. Model Design Strict separation between
GAMS: generic model code
Excel: application-specific files that contain the database (general; MDG) and the specification of simulations
A user-friendly interface, ISIM-MAMS, has been developed.
GAMS code covers everything that is common across applications.
Each database controls the model disaggregation, selection of version (core or extended to all or part of modules of MDG versions), the time frame for simulations, and selected assumptions.

7. Model Structure
Open-economy recursive-dynamic real model in the World Bank/Robinson tradition.
Core module + MDG module (in full or only selected parts) and/or poverty module.
MAMS may be solved in “multi-pass” mode (year by year) or in “single-pass” mode (simultaneously for all periods; often faster but less robust).
MCP (Mixed-Complementary Program) solver.

8. Structure of MAMS
The following figure summarizes the payment flows that are captured by MAMS in any year.
Main building blocks:
Activities (producers)
Institutions: Households, Government, Rest of World
Markets: factors, domestic commodities
Most blocks are typically more disaggregated.

9. Figure shows payment flows for one year for economic core (not MDGs, not dynamics); Often real flows in the opposite direction
The main building blocks
Activities: carry out production in a year, maximizing profits (not enterprises)
Markets for factors (labor, capital, land) and domestically for commodities (goods and services)
Institutions: Rest of world (appears in the BoP); (General) government ; Households (domestic non-government institutions
In most applications most “blocks” are further disaggregated. Exceptions: RoW and government.
All blocks are subject to consistency (budget) constraints. For each block, one “clearing variable”
Activities (look at arrows)
Outlays. Profit maximization  factor hiring and intermediate input purchases; output;
Receipts. Output paid for from “domestic commodity markets” and “rest of world”; profit maximization  reallocation of sales between exports and domestic markets in response to relative price changes
Households
Receipts. (a) factors (endowments); (b) transfers + interest from government; (c) transfers – interest from Row;
Outlays. (a) (direct) taxes; (b) private savings (part of which is lent to government); (c) private consumption; . Gov decides dir tax rates; savings rates = f(per-capita income, demography); (disaggregated) consumption = f(net income, relative prices)
Closure rule (clearing variable). By construction, household consumption demand functions will generate spending equal to net income available for consumption.
Government
Receipts. Taxes (direct and indirect); (net) transfers from RoW (net of interest on foreign debt)
Outlays. Government consumption, government investment (with supplementary financing from lending from households and RoW); transfers to households (incl. interest on domestic debt).
Closure rule (clearing variable): Adjustment on the receipt side (taxes, transfers) or on the spending side (one or more components of consumption and/or investment)
Rest of the world.
Receipts (the outlays of the model country). Imports; factor incomes
Outlays (the receipts of the model country). Exports, transfers (net of interest in foreign debt) to government and households; FDI; (net) lending to supplement private and government investment financing.
Closure rule (clearing variable). Real exchange rate (appreciation discourages exports, encourages imports; v.v. for depreciation.
Private investment financing.
Receipts. Private savings (net of lending to government), FDI, and net lending from RoW to private (household) sector.
Outlays. Private investment spending.
Closure rule (clearing variable). Either private investment level (driven by available financing); or household (private savings; if some rule is imposed for private investment)
Factor markets. Clearing via wage adjustment; without endogenous unemployment [vertical supply curve] or with endogenous employment [upward-sloping (wage) curve].
Domestic commodity markets. Given exchange rate, world prices, and domestic prices, domestic producers (activities) and domestic demanders decides on quantities supplied and demanded of domestic commodities. The domestic market prices is flexible, clearing the market.

10. Activities Sell their output at home or abroad.
Use their revenues to cover their costs.
Produce to maximize profits 
Factor hiring and other input use depend on wages, input prices, output prices
Output shares exported and sold domestically depend on the relative prices of output in world and domestic markets.

11. Activities Each activity produces a “commodity” (good or service).
Additional commodities are non-competitive imports (i.e. without domestic production).

12. Households
Earn incomes from (a) factors; (b) transfers and interest from loans to the government (with the interest due to loans from the households to the government); and (c) transfers from the rest of the world net of interest on household foreign debt (tracked by model).
Use incomes for direct taxes, savings, and consumption.

13. Households Savings shares depend on per-capita incomes.
Consumption decisions change in response to income and price changes.
By construction (and as required by their budget constraints), the consumption value of the households equals their income net of direct taxes and savings.

14. Government The government
gets its receipts from taxes, domestic and foreign transfers, and foreign borrowing.
uses these for services (=government consumption), investments (providing the capital stocks required to produce these services), transfers to households, and interest payments.
The model tracks of government domestic and foreign debt stocks (including foreign debt relief).

15. Government
Each receipt and spending item follows some rule (with plenty of options – exogenous values, share of GDP or absorption, rates …)
Government follows a “closure rule”, indicating how it remains within its budget constraint (adjusting one or more items on the spending or receipt side).

16. The rest of the world (RoW)
Is represented in the balance of payments.
Provides foreign currency in the context of transfers to government, and households (net of interest payments on foreign debts), FDI, net loans, and exports.
Receives foreign currency in exchange for imports.
Imports take place at exogenous world prices.
For exports, the alternative of an export demand function is available.

17. The rest of the world
Export and import decisions are made by domestic producers and demanders, resp.
Non-trade payments follow specified rules (with different options).
The “budget” of the RoW (the balance of payments) follows a “closure rule”: adjustments in the real exchange rate equalize inflows and outflows of foreign currency (by influencing exports and imports).
The real exchange rate = the ratio between the international and domestic price levels.

18. Private investment financing
It is provided from domestic private savings (net of lending to the government) and foreign direct investment (FDI).
For the private savings-investment balance, the closure rule is either that investment spending adjusts in response to changes in available funding or that savings adjust to an exogenous spending level.

19. Domestic commodity markets
Domestic demanders decide on import and domestic shares in their demands on the basis of the relative prices of commodities from these two sources (foreign and domestic).
Domestic suppliers (the activities) decide on the shares for exports and domestic supplies on the basis of the relative prices received in these two markets (foreign and domestic).

20. Domestic commodity markets
Flexible prices ensure balance between demands for domestic output from domestic demanders and supplies to the domestic market from domestic suppliers.

21. Markets for factors (labor, capital, natural resources, …)
Reach balance between demands and supplies via wage (or rent) adjustments.
Factor demand curves are downward-sloping reflecting the responses of production activities to changes in factor wages.
For most factors, within-period supplies are exogenous.

22. Markets for factors
Optional endogenous unemployment for labor: a wage curve (a supply curve) is upward-sloping until full employment is reached – see figure.
“Unemployment” is defined more broadly than in official statistics to include un- and under-employment – it should capture the scope for the existing labor force to generate a larger amount of effective labor (if the incentives to work were to improve).

23. Factor market with endogenous unemployment

24. MDG “Production”
The MDGs are “produced” by a combination of determinants (including government social services; see table) using a (reduced) functional form that permits:
replication of base-year values and elasticities
calibration to additional point (typically one possible set of conditions under which the MDG in question is achieved)
imposition of limit (maximum or minimum)
diminishing marginal returns to the inputs

25. Determinants of MDG Outcomes (X)
For MDG analysis, classification of government demand by function: social services (education, health, water-sanitation), infrastructure, and “other government”.
Determinants of MDG Outcomes (X)

26. MDG outcomes Two-level functions: Logistic function
constant-elasticity function at the bottom: Z = f(X)
logistic function at the top: MDG = g(Z)
Logistic function
Logistic function

27. Education and Labor
Typically, education is divided into three levels: primary, secondary, and tertiary.
At each level, model generates
enrollment
rates of primary net intake, promotion, dropout, repetition, continuation to next cycle
At each level, outcomes are determined by services per student and other determinants (similar to MDG table).

28. Dynamics: Over time growth is due to …
growth in factor stocks (shifting factor supply curves), determined by
investment and depreciation (capital stocks)
demography and educational system (labor)
exogenous trends (other factors)
growth in total factor productivity (TFP), with components that are
endogenous (government capital stocks, openness to trade); and
exogenous (trend term)

29. Top-Down Poverty Analysis
Microsimulation or built-in poverty module
Built-in poverty module generates poverty and inequality results that are fully integrated with the MAMS simulations:
constant elasticity of poverty with respect to per-capita welfare for each model household
log-normal distribution of per-capita welfare within each model household
distribution of per-capita welfare within each model household follows a real-world household survey.

30. Common simulations Policies:
Level and composition of government and consumption and related investments.
Levels of foreign grants to government (a tool from the perspective of the rest of the world).
Other financing: taxes, domestic and foreign borrowing.
MDG targeting
Other shocks: technology (including government efficiency), external environment.

31. Data Requirements
SAM in MAMS format (including institutional capital accounts).
Disaggregation of MDG- and education-related services needed for MDG version.
Elasticities for trade, consumption, production.
MDG and education outcome elasticities.
MDG and education calibration points.

32. User-Friendly Interface
ISIM-MAMS = GAMS program + Interface.
The user defines and runs MAMS simulations in an Excel 2007 or 2010 environment.
The MAMS Interface is connected to a database that stores:
data elements specific to the country dataset and/or be needed to define scenarios
set elements: commodities, activities, factors, institutions, etc.
default elasticities and closure and rules/policies

33. User-Friendly Interface
The user-defined scenarios are saved as part of the ISIM-MAMS application Excel file.
Advanced users (“Expert Mode”) can change and create of application datasets for ISIM-MAMS.

34. User-Friendly Interface
ISIM-MAMS = GAMS program + Interface.
The user defines and runs MAMS simulations in an Excel 2007 or 2010 environment.
The MAMS Interface is connected to a database that stores:
data elements specific to the country dataset and/or be needed to define scenarios
set elements: commodities, activities, factors, institutions, etc.
default elasticities and closure and rules/policies

35. User-Friendly Interface: Screen Captures

36. Policy Issues and Insights
Two main types of simulations:
full achievement of key MDGs by 2015 (fix targets year to year; flex policy tool) with alternative financing mechanisms;
alternative scenarios for public spending (in terms of total resource envelopes and sector priorities), financing (domestic and foreign), and efficiency of public service production and delivery

37. Policy Issues and Insights
Spending on HD vs. infrastructure.
Infrastructure has more positive growth impact while also having positive HD effects.
Balanced scenarios more attractive in terms of outcomes and politics.
Income distribution. Scaled-up HD spending raises educated wages except for long run when this reverses.

38. Policy Issues and Insights
Domestic financing vs. foreign aid. Aid pushes difficult trade-offs to the side.
Foreign aid and Dutch disease. Strength of DD effect depends on the marginal import share of government spending; effect is stronger for HD-focused scenarios.
Government allocative efficiency. Strong gains from moderate reallocations of spending growth from areas with small or no returns.

39. Yemen Application: Data
Key elements of the database:
a 2004 Social Accounting Matrix for Yemen
data on MDGs, education, and the labor market (including MOPICs MDG Needs Assessment)
selective estimation of elasticities
MAMS was combined with a microsimulation methodology to estimate poverty and inequality effect using microdata from household survey.

40. Yemen Application: Scenarios

41. Yemen Application: Growth

42. Yemen Application: MDG 4 (U5MR)

43. References
Lofgren, Hans, Martin Cicowiez, and Carolina Diaz-Bonilla, “MAMS – A Computable General Equilibrium Model for Developing Country Strategy Analysis”. pp. 159–276 in Dixon, Peter B. and Dale W. Jorgenson, (Eds.), Handbook of Computable General Equilibrium Modeling. North Holland, Elsevier B.V.
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