Instead, the demographic transitions experienced by a wide variety of societies suggest that family sizes tend to decline with higher incomes and greater economic security. Conversely, poor families tend to have more children in the hope of increasing contributions to household income as well as of ensuring continued economic security as parents age (Leibenstein, 1957, Mamdani, 1972, Robbins, 1999). A significant proportion of this decline can be largely attributed to the rise in living standards in East Asia and the Pacific which accompanied explosive economic growth, particularly in China. Other regions of the world also experienced a decline in the incidence of poverty, with the exception of Eastern Europe and Central Asia, where the proportion of people living on less than $1.25 a day increased from 1.7 to 3.7 per cent between 1981 and 2005 (figure II.2.B).