Just how bad is a country's debt for growth

Yes I know that I have a previous entry on the effects of public debt on economic growth. That, however, only focused on South Africa.

Once again public finances bother me. I can't quite wrap my head around why some countries are able to sustain such large amounts of debt and not be in any danger (according to rating agencies) of default while other countries with comparably smaller debt are at risk of defaulting. The common marcro reasons cited for this are long-term growth rates, low interest on bonds, little debt denominated in foreign currency, the maturity of debt and stable and low inflation. Political factors are also important. These include weeding out corruption, have proper expenditure plans in place and don't have domestic strife (investors seem to hate this).

I wish I had time to do a counter-factual and determine how better or worse a country would have been without increasing its sovereign debt. For now we will have to settle with a (hopefully) interesting figure just to get us interested. The scatterplot illustrates the relationship between debt and economic growth for advanced and emerging economies (five year averages from the IMF). A striking feature of the figure is that there is a negative relationship between economic growth and low debt. There is a positive relationship between debt and economic growth for advanced economies between 25%-50% of debt to GDP. Higher values of debt/GDP >50% seems to have a negative effect on economic growth. For EM countries the positive relationship between debt and GDP occur between 35%-100% of debt/GDP. This is indeed a very big range.

What this figure tells us is that aggregating numbers like this tells us very little about the real effects of debt. To really understand the consequences of accumulating debt one has to look at a lot of micro factors (the reasons for accumulating debt, the maturity of debt, etc.). This would be difficult to accomplish since many countries hardly report these variables necessary to do any useful analysis. There is also no reason to believe that debt thresholds are static. The evolution of fiscal policy and the macroeconomic landscape change frequently. We should expect that these thresholds would also change.