2010年-世界发展银行全球_The_Impact_of_Infrastructure_Spending_in_Sub-Saharan_Africa___A_CGE_Modeling_Approach_57页_924kb

Summary of "The Impact of Infrastructure Spending in Sub-Saharan Africa: A CGE Modeling Approach"

Core Content

This working paper by Jean-François Perrault, Luc Savard, and Antonio Estache explores the economic impact of increased infrastructure spending in six Sub-Saharan African countries: Benin, Cameroon, Mali, Senegal, Tanzania, and Uganda. The authors use a computable general equilibrium (CGE) model to simulate various infrastructure investment scenarios and their fiscal implications. The model incorporates infrastructure externalities, which are sector-specific and influence overall productivity and economic outcomes.

The study examines four types of infrastructure investment:

• Nonproductive infrastructure
• Road infrastructure
• Electricity infrastructure
• Telecom infrastructure

For each investment type, five funding schemes are considered:

• Reduced public expenditure
• Increased value-added taxes
• Increased import duties
• Funding from foreign aid
• Increased income taxes

The paper also introduces a sectoral analysis of the economic structure of the six countries and how different infrastructure investments affect welfare, macroeconomic variables, and distributional outcomes.

Main Views and Key Findings

1. CGE Model Overview

• The model is based on the EXTER framework, adjusted to include infrastructure externalities.
• It features seven sectors: food crop agriculture, export agriculture, mining and oil, manufacturing, construction, private services, and public services.
• The model allows for:
  • A detailed analysis of sectoral effects.
  • Fiscal policy simulations to fund infrastructure investment.
  • A comparative analysis of how different funding sources affect macroeconomic outcomes.

2. Sectoral Characteristics

• The labor/capital ratio is a key determinant of how infrastructure investment impacts different sectors.
• Export/output ratios vary significantly by sector and country, reflecting different economic structures.
• Construction and industries are generally more capital-intensive, while agriculture is more labor-intensive.
• Private services are a significant part of the economy in some countries (e.g., Benin), but not in others (e.g., Tanzania).

3. Funding Schemes and Their Effects

• Funding schemes generally have similar qualitative effects on macroeconomic variables.
• However, quantitative differences are notable, especially for road and electricity investments.
• Foreign aid is the most effective in balancing the current account, as it allows for strong price and exchange rate adjustments.
• Taxation policies (income, value-added, import duties) also play a role in shaping the distributional impact of infrastructure investment.

4. Infrastructure Externalities

• Infrastructure investment can lead to positive externalities that improve total factor productivity.
• The externality function is defined as a sector-specific elasticity of the ratio of new investment to past investment.
• The impact of infrastructure is not uniform across sectors, as the degree of openness to trade varies.

5. Sectoral Analysis and Country Differences

• The economic structure of each country influences how infrastructure investment affects different sectors.
• Uganda is used as a case study to assess whether its scenario is special or typical of other African countries.
• The capital/labor ratio of each sector plays a key role in determining winners and losers of the investment scenarios.

6. Model Equilibrium and Assumptions

• The model assumes world prices are exogenous, and factor allocations are fixed.
• The government budget constraint is balanced by adjusting public expenditure and taxation.
• Public investment is linked to operation and maintenance costs, which vary by infrastructure type and region.
• The externality parameter $(\omega)$ is used to adjust the impact of infrastructure investment based on its type and the economic context.

Key Information

Countries Studied

Sectoral Weights in GDP

Infrastructure Externalities

• The externality parameter $(\xi_i)$ is used to model the sector-specific productivity effect of infrastructure investment.

• The externality function is:
  $$
  \theta_i = \left(\frac{Itp}{Itpo}\right)^{\xi_i}
  $$
  where $Itp$ is current public investment and $Itpo$ is past investment.

• The value-added function is:
  $$
  Va_m = \theta_i A_m Ld_m^{\alpha_m} Kd_m^{1 - \alpha_m}
  $$
  where $A_m$ is the scale parameter, $Ld_m$ is labor demand, $Kd_m$ is capital demand, and $\alpha_m$ is the Cobb-Douglas parameter.

Externality Elasticities

Conclusion

The study demonstrates that infrastructure investment has varying impacts depending on:

• The type of infrastructure (roads, electricity, telecoms, etc.)
• The economic structure of the country
• The funding source used to finance the investment

The CGE model provides a robust framework for analyzing these impacts, and the sectoral analysis highlights the heterogeneity of economic structures and responses to infrastructure spending. The use of foreign aid is particularly effective in balancing the current account and generating sectoral productivity gains, while taxation policies and public expenditure adjustments also play a significant role in shaping the fiscal sustainability and distributional outcomes of infrastructure investment.