Returns to international research investment ranged from 68 to 108 per cent (Evenson and McKinsey Jr., 1991).10 While the returns to R&D are high, several factors prevent them from having the kind of impact on LDC agricultural productivity that would bring them even remotely close to their potential. The Agricultural Science and Technology Indicators compiled by the International Food Policy Research Institute (IFPRI) show that the sector’s agricultural research spending relative to its gross domestic product (GDP) — the research intensity ratio — is substantially lower than in advanced economies. In 2008, low-income countries spent only $0.44 (at 2005 purchasing-power parity (PPP)) on public agricultural R&D for every $100 of agricultural GDP. The corresponding figure for high-income countries was more than $3 (chart 2.10). The average intensity ratio for low-income countries has declined marginally over the past 35 years, meaning that growth in R&D spending has lagged behind the expansion of agricultural GDP. In high-income countries, by contrast, public agricultural R&D spending for every $100 of agricultural GDP (2005 PPP) has risen steadily since the early 1980s, reaching $2.63 in 2000 and $3.07 in 2008.