The BOOST program was launched in 2010 as a platform for improving, standardizing and curating data collection associated with the World Bank’s Public Expenditure Reviews in countries. It tracks wellclassified and highly disaggregated budget data derived from engagements with individual countries in a country-specific manner. The BOOST database covers the period 2006 - 2018. The sample is quite unbalanced, with many earlier year observations missing. Furthermore, the available sample shrinks at increasingly fine levels of disaggregation. While aggregate public expenditure is available for over 70 countries, the number shrinks to 61 countries when looking at disaggregated expenditure for roads, and 46 countries for disaggregated expenditure on electricity. Coverage is also uneven depending on the subcategory of data considered, with greater availability of data on investments than on recurrent expenditure, and even less on subsidies. Combining BOOST data with other sources to build a wider picture of on- and off-budget expenditure further reduces the sample due to limited overlap in countries for which multiple data sources are available.

An important issue is differences between countries in the institutional coverage of the budget data provided. While 36 of the countries provide General Government data, which includes expenditure by subnational authorities, the remaining 41 countries provide only Central Government data. Examination of the General Government data shows that for most countries subnational expenditure represents no more than 6 percent of the General Government total, except in federal states. This suggests that pooling General Government and Central Government data is a defensible approximation, particularly for relatively small and unitary states as long as large federations supplying only Central Government data are excluded.<sup>4</sup> To build up a comprehensive picture of on-budget and off-budget expenditure, it is essential to combine BOOST data with other sources of information that capture development aid as well as domestic spending through off-budget vehicles. When aggregating these different sources of data some possibility of doublecounting is introduced, across some though not all of the categories. Wherever possible this issue is examined and any double-counting directly addressed through subtraction. However, due to data limitations this is not always possible. Table A2.5 qualitatively identifies the nature of the risks across each pair of categories. Since double-counting cannot be entirely eliminated, the resulting aggregate estimates must be considered as an upper bound. Given how low the resulting spending envelopes are relative to estimates of spending needs, this does not, however, affect the main conclusions of the paper.

The BOOST database does not capture foreign capital spending such as contributions made by multilateral, bilateral or other donor institutions, because these are typically not channeled through the budget. This source of funding plays an important role in infrastructure financing in the developing world and needs to be incorporated to get a complete picture. The OECD DAC database covers donor and multilateral commitments to developing countries across sectors. The database covers disbursements to 155 countries (from 29 donors) over the period 2005 – 2019. However, the OECD DAC database does not cover financing contributions by Non-Paris Club Members, notably China, which has become a significant source of infrastructure finance for some developing countries (Malik et al., 2021). Therefore, this study also draws upon the College of William and Mary’s AidData database that captures over 13,000 officially-financed Chinese projects (by Chinese government institutions and state-owned entities) in five regions (Africa, the

> 4 These considerations led to the exclusion of Argentina and Brazil from the BOOST analysis, due to the fact that they are large federal states known to have substantial infrastructure expenditure at the sub-national level, yet only reported central government expenditure to BOOST.

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