A student finds major mistakes in a famous paper by 2 Harvard economics professors.

Carmen Reinhart and Ken Rogoff "Growth in a Time of Debt" supposedly showed that "economic growth slows dramatically when the size of a country's debt rises above 90% of Gross Domestic Product, the overall size of the economy." 

Some key figures tackling the global recession found this paper a useful addition to the debate at the heart of which is this key question: is it best to let debt increase in the hope of stimulating economic growth to get out of the slump, or is it better to cut spending and raise taxes aggressively to get public debt under control?

EU commissioner Olli Rehn and influential US Republican politician Paul Ryan have both quoted a 90% debt-to-GDP limit to support their austerity strategies.

But the calculation was wrong.