If your debt rises above a certain proportion of your annual income, and income is growing slowly, most credit-raters would hesitate to give you a good rating. The same applies to companies and countries. Look at the graph and you see things arent quite as simple. In the case of the US, which has just had its ratings outlook changed by Standard & Poors, the debt profile doesnt seem to warrant the rating. The dollar being the global reserve currency gives the US a kind of leverage no other country has, but is there more to it Chinas debt profile and relative ranking suggests there may be.