To analyze the effect of an increase in the quantity or quality of public investment on growth, this paper extends the World Bank's Long-Term Growth Model (LTGM), by separating the total capital stock into public and private portions, with the former adjusted for its quality. The paper presents the Long-Term Growth Model Public Capital Extension (LTGM-PC) and accompanying freely downloadable Excel-based tool. It also constructs a new Infrastructure Efficiency Index (IEI), by combining quality indicators for power, roads, and water as a cardinal measure of the quality of public capital in each country. In the model, public investment generates a larger boost to growth if existing stocks of public capital are low, or if public capital is particularly important in the production function. Through the lens of the model and utilizing newly-collated cross-country data, the paper presents three stylized facts and some related policy implications. First, the measured public capital stock is roughly constant as a share of gross domestic product (GDP) across income groups, which implies that the returns to new public investment, and its effect on growth, are roughly constant across development levels. Second, developing countries are relatively short of private capital, which means that private investment provides the largest boost to growth in low-income countries. Third, low-income countries have the lowest quality of public capital and the lowest efficient public capital stock as a share of gross domestic product. Although this does not affect the returns to public investment, it means that improving the efficiency of public investment has a sizable effect on growth in low-income countries. Quantitatively, a permanent 1ppt GDP increase in public investment boosts growth by around 0.1-0.2ppts over the following few years (depending on the parameters), with the effect declining over time.

To analyze the effect of an increase in the quantity or quality of public investment on growth, this paper extends the World Bank’s Long-Term Growth Model (LTGM), by separating the total capital stock into public and private portions, with the former adjusted for its quality. The paper presents the LTGM public capital extension and accompanying freely downloadable Excel-based tool. It also constructs a new infrastructure efficiency index, by combining quality indicators for power, roads, and water as a cardinal measure of the quality of public capital in each country. In the model, public investment generates a larger boost to growth if existing stocks of public capital are low, or if public capital is particularly important in the production function. Through the lens of the model and utilizing newly-collated cross-country data, the paper presents three stylized facts and some related policy implications. First, the measured public capital stock is roughly constant as a share of gross domestic product (GDP) across income groups, which implies that the returns to new public investment, and its effect on growth, are roughly constant across development levels. Second, developing countries are relatively short of private capital, which means that private investment provides the largest boost to growth in low-income countries. Third, low-income countries have the lowest quality of public capital and the lowest efficient public capital stock as a share of GDP. Although this does not affect the returns to public investment, it means that improving the efficiency of public investment has a sizable effect on growth in low-income countries. Quantitatively, a permanent 1 ppt GDP increase in public investment boosts growth by around 0.1–0.2 ppts over the following few years (depending on the parameters), with the effect declining over time.

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The Policy Research Working Paper Series disseminates the findings of work in progress to encourage the exchange of ideas about development issues. An objective of the series is to get the findings out quickly, even if the presentations are less than fully polished. The papers carry the names of the authors and should be cited accordingly. The findings, interpretations, and conclusions expressed in this paper are entirely those of the authors. They do not necessarily represent the views of the International Bank for Reconstruction and Development/World Bank and its affiliated organizations, or those of the Executive Directors of the World Bank or the governments they represent.

As some emerging market economies have amassed large quantities of foreign exchange reserves, concern has arisen over the sterilisation of the domestic money stock from these flows. Existing studies focus mostly on narrow (reserve) money, and estimate a high degree of sterilisation. Empirical work on the long-run relationship between money and prices emphasises broad money, yet the long-run effect of foreign exchange inflows on broad money has been almost entirely ignored. Using a sample of quarterly data from 28 countries over the period 1990-2010, it is shown that broad money is sterilised to a significantly smaller degree than reserve money, raising concerns about the implications for financial imbalances and inflation. This pattern of sterilisation is not confined to any particular group of countries and is unrelated to the nature of the flows (e.g. current account versus capital account surpluses). Sterilisation rates have increased in Asia during the recent period of persistent accumulation of foreign exchange reserves.