US rating agency Standard & Poor's last night revised Japan's sovereign credit rating to negative, but traders appear unconcerned by the move despite figures showing the Japanese deficit is well above levels that would normally set alarm bells ringing.

This chart, published last week by Deutsche Bank analysts, shows the public debt burden of various countries relative to their gross domestic product. The dotted line in the middle shows the point at which this hits 100%, which academics Reinhart and Rogoff identified as the point at which debt begins to have negative implications for growth.