estimates make sense, we use data from World Bank (2010) to calculate net income, and then apply expression (2) in order to derive the implicit rate of return on comprehensive wealth in each country. The distribution of rates of return is plotted in Figure 1, which shows that 80% of the rates lie between 4% and 6%.

Produced capital stocks are derived from historical investment data using a perpetual inventory model. Most natural resources are valued by taking the present value of resource rents—the economic profit on exploitation—over their assumed lifetime. Resources considered include energy, mineral, timber and non-timber forest resources, cropland, pastureland and protected areas.

Finally, the wealth estimates in World Bank (forthcoming) account for ownership of capital. The interest payments derived from foreign financial assets or obligations will affect future levels of consumption of the country's residents and, by construction, total wealth. The adjustment to the wealth estimates to account for ownership is particularly important in the light of the acceleration in cross border asset trade observed in the last decades.<sup>5</sup> By definition intangible capital includes any asset other than physical capital, natural resources and net foreign assets. It thus includes human capital—the sum of knowledge, skills, and knowhow possessed by the population. It includes the institutional and social infrastructure of the country. It also includes resources omitted in the natural capital calculations such as subsoil water, diamonds, and fisheries.<sup>6</sup> Table 2 presents descriptive statistics of total wealth and its components. Our sample includes an unbalanced panel of 115 developed and developing countries for years 1995, 2000 and 2005 (total of 315 observations). All the numbers in Table 2 are expressed in per capita terms in constant 2005 US$. For most countries in our sample, intangible capital is the largest component of total wealth; on average it constitutes 64 percent of total wealth, although it varies from a minimum of 5 percent in Uganda to a maximum of 90 percent in St. Lucia. Figure 2a shows that intangible capital is positively correlated with income. This is not surprising. As shown in Panel B of Table 2, except for net foreign assets, richer countries have, on average, more capital than

> rate, the expression for total wealth can be simplified to _W_   _C_ ( _t_ )  _e_  ( _s_  _t_ ) _ds_ , where _ρ_ , the pure rate of time  _t_ preference, is assumed to equal 1.5 percent. For more details please see World Bank (forthcoming). 5 An indicator of financial integration used by Lane and Milesi-Ferretti (2007), the sum of external assets and liabilities over GDP, has risen steadily in both developing and developed countries, more markedly in the latter, where it increased by a factor of 7, from 45% in 1970 to over 300% in 2004, with a clear acceleration in the mid 1990s.

> 6 Owing to data limitations no explicit value for ecosystem services is estimated. However, the services provided by ecosystems, such as the hydrological functions of forests and the pollination services of insects and birds, are indirectly captured in the natural wealth estimates through the values of cropland and pastureland.

5