Rome, January 8 - Italy's deficit/GDP ratio was an average 2.9% in the first nine months of 2015, 0.4% better than the same period in 2014 when it was 3.3%, Istat said Friday. In the third quarter the ratio was 2.4%, the statistics agency said. Italy posted a primary surplus of 1.3% of GDP over the first nine months of 2015 compared to 1.4% in the same period of 2014, Istat said. Italy's tax burden rose 0.1% to 41.4% in the third quarter of 2015 compared to the same quarter in 2014, Istat said. Over the first nine months of the year, the tax burden averaged out ar 41.2%, steady compared to the same period in 2014.