Year	% of total
1970	86.49617360135366
1971	86.98907424084318
1972	86.67303400197324
1973	86.59415257879337
1974	86.20820284603663
1975	85.39167334322184
1976	84.8446252363104
1977	84.9432696518393
1978	84.60492099978862
1979	84.22391863504687
1980	84.1080081688572
1981	83.557096067778
1982	83.45137600004063
1983	83.8951952568938
1984	84.09240821443566
1985	84.05652164723783
1986	84.1731069611063
1987	84.2339089606605
1988	83.63608890868109
1989	83.29274850207405
1990	90.52631578947368
1991	83.16151202749141
1992	81.17647058823529
1993	78.29787234042553
1994	77.13004484304933
1995	75.89285714285714
1996	75.46296296296296
1997	76.2114537444934
1998	76.52173913043478
1999	77.21518987341773
2000	77.31092436974791
2001	78.98832684824903
2002	79.5539033457249
2003	79.78339350180505
2004	80.3448275862069
2005	80.33898305084746
2006	80.84415584415584
2007	80.64516129032258
2008	81.45896656534954