Several tax increases instituted by the federal government between 1989 and 1991 were another key cause of Canada's recession. These increases related to sales, excise and payroll taxes were modelled to have reduced real GDP growth by 1.6, 2.4 and 5.1 percentage points, respectively, in 1990, 1991 and 1992, although if these tax increases had not been implemented the federal governments national debt would have increased a significant amount. A third, less important factor in Canada's recession was the weakness of the US economy at the time, which was calculated to have had the effect of reducing Canada's economic growth by .6, 2.2 and 1.1 percentage points in 1990, 1991 and 1992.