Are global credit rating agencies unfair to governments in emerging markets? Such complaints are not unknown. The finance ministry came up with a Comparative Rating Index of Sovereigns that tried to offer a different narrative. Chinese credit rating agency Dagong even downgraded the US in October.

A controversial paper published in December by two economists at the University of Heidelberg raises strong questions on how governments are rated. It shows that four of the nine credit rating agencies they looked at provide a much higher rating for countries where their headquarters are based. The economists have studied ratings of 143 sovereign issuers. Naturally, this is not a finding the ratings agencies have liked.

Major rating agencies lost face when the global financial crisis showed how they had lavished strong ratings on mortgage-backed securities. Yet their assessments still carry weight in financial markets. Emerging market bonds are under particular pressure during threats of a sovereign downgrade.