The neoclassical growth model predicts that developing countries with faster productivity growth should invest more and attract more foreign capital. Gourinchas and Jeanne (2013) documented the opposite: across developing countries, capital does not flow more to the countries that invest and grow more, a pattern they named the 'allocation puzzle'. Wedge accounting shows the pattern is driven by national saving rather than by investment, and it is linked to public capital flows, especially the accumulation of international reserves, and is stronger in more financially open economies. The authors state that the main explanation remains an open question and leave a road map of undiscriminated candidate mechanisms. The problem is to identify and empirically discriminate among the mechanisms - saving-side frictions, reserve-accumulation motives, domestic financial frictions, precautionary behavior, and policy regimes - that generate the observed growth-saving-reserve nexus, including why public reserve accumulation in high-growth countries is not offset by private capital inflows. No consensual resolution of the problem is known in the literature to date, and contributions through 2025 continue to treat the question as open.

Background

A central prediction of the neoclassical growth model is that capital should flow toward countries where it is scarce and returns are high: a developing country whose total factor productivity (TFP, the share of output growth not explained by the accumulation of labor and capital) grows faster should invest more and, if its capital account is open, finance part of that investment with foreign savings, running a current account deficit (the current account is the negative of net capital inflows from abroad). Robert E. Lucas Jr. famously asked why aggregate capital does not flow from rich to poor countries in this way (the 'Lucas paradox'). Gourinchas and Jeanne (2013) sharpened the question within the developing world: in a sample of developing economies, capital does not flow more to countries that invest and grow more - if anything it flows less. They called this the 'allocation puzzle'.

To locate the failure, the authors use wedge accounting: they insert a 'saving wedge' (a distortion that shifts national saving) and an 'investment wedge' (a distortion that shifts investment) into an otherwise standard growth model and calibrate each so that the model reproduces the observed capital flows of each country. The calibrated saving wedges, not investment wedges, line up with productivity growth: fast-growing countries save too much relative to the benchmark. The allocation puzzle is therefore a saving puzzle. Disaggregating the balance of payments further shows the pattern is tied to public capital flows, in particular the accumulation of international reserves (foreign-currency and other liquid external assets held by a country's government or central bank), and it is stronger, not weaker, in economies more open to international finance.

This last fact contains an embedded sub-puzzle. In a frictionless benchmark with Ricardian equivalence (the principle that public and private saving decisions offset one another, so how the saving is split between government and households does not matter for the total), an accumulation of foreign assets by the public sector should be offset by private capital inflows: the country as a whole would still borrow from abroad if returns warranted. Yet in high-growth developing countries public reserve accumulation is not offset by private inflows, even where financial openness would permit it.

The paper's concluding discussion reviews five families of candidate explanations without discriminating among them empirically: (1) consumption habits, in which households save more when growth rises because consumption adjusts sluggishly to income (Carroll, Overland and Weil, 2000); (2) domestic financial frictions that prevent residents from borrowing against future income or from storing value at home, or that channel savings into foreign assets (Gertler and Rogoff, 1990; Matsuyama, 2004; Caballero, Farhi and Gourinchas, 2008; Song, Storesletten and Zilibotti, 2011); (3) precautionary saving, in which faster growth goes together with more uninsured idiosyncratic risk or more exposure to sudden stops (abrupt reversals of capital inflows), so households or entrepreneurs self-insure by accumulating safe foreign assets (Carroll and Jeanne, 2009; Sandri, 2014); (4) the 'Bretton Woods 2' policy view, under which governments of high-growth countries deliberately resist currency appreciation and accumulate reserves as part of an export-led development strategy (Dooley, Folkerts-Landau and Garber, 2003); and (5) political-economy models in which limited commitment by governments forces the public sector to reduce external liabilities along the growth path (Aguiar and Amador, 2011). The authors state explicitly that the main explanation or explanations remain, in their view, an open question, and describe their concluding discussion as a tentative road map for research rather than new results.

Problem Statement

Following Gourinchas and Jeanne (2013), the open problem is to explain the allocation puzzle: to identify the economic mechanism or mechanisms that generate the negative cross-country correlation between productivity growth and net capital inflows among developing countries - a pattern that wedge accounting attributes to national saving and that is tied to public capital flows, especially the accumulation of international reserves, and is stronger in more financially open economies - and to discriminate empirically among the candidate explanations (habit-based saving, domestic financial frictions, precautionary saving against idiosyncratic and aggregate risk including sudden stops, the Bretton Woods 2 policy view, and political-economy models of limited commitment). Explaining the pattern further requires accounting for the compositional evidence on public versus private flows and on foreign direct investment versus portfolio flows, and for why public reserve accumulation in high-growth countries is not offset by private capital inflows even in financially open economies, contrary to the Ricardian-equivalence benchmark.

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