摘要：The demand for food in any given country or region depends on several factors, among which are income, cultural preferences and the number and age of its inhabitants. Thus population projections form a crucial input into models of future demand for food and other agricultural products. Fortunately, given this importance, population forecasts can be reasonably reliable. As Ron Lee puts it, "On average people live long lives, have a long lag between birth and childbearing, and experience demographic rates with highly regular age patterns. These patterns change quite slowly. For these reasons, population is reliably predictable over fairly long periods compared to economic performance or the weather. Nonetheless, demographic forecasting does involve a good deal of uncertainty." (Lee 1999, 156).
