One in five Arabs still live on less than $2 a day. And over the past 20 years growth in income per head, at an annual rate of .5%, was lower than anywhere else in the world except sub-Saharan Africa. At this rate, says the report, it will take the average Arab 140 years to double his income, a target that some regions are set to reach in less than 10 years. Stagnant growth, together with a fast-rising population, means vanishing jobs. About 12 million people, or 15% of the labor force, are already unemployed, and on present trends the number could rise to 25 million by 2010.