Estimating the extent of the D.P.R.K.'s economic decline is problematic-Pyongyang is simply not very generous with statistics. What we do know is that many hungry people are willing to risk their lives to try to cross the Yalu River, which separates China and the D.P.R.K.There are also more measurable indicators that show how bad things are. North Korea's 2006 national budget was just $2.9 billion-an estimated 16 percent of which was spent on the military. And in South Korea, where average incomes are now 15 times higher than in their northern neighbor, the 2005 GDP was $1.18 trillion, while the North's was, at best, $40 billion. In fact, the gap between the two Koreas is widening in just about every applicable category-life expectancy, caloric intake, incidence of disease, and even average height.Now the job of propping up the D.P.R.K. has fallen to China, which is the country's largest donor of coal, electricity, gasoline, and grain. The D.P.R.K. now accounts for more than one-third of China's international aid budget. China hopes that if it keeps North Koreans alive, they will stay in North Korea; a flood of millions of refugees is just too horrible for Beijing to contemplate.