Year	% of total
1970	74.84707892193227
1971	75.84509373025969
1972	75.67829993389695
1973	76.51858617082729
1974	75.7242052656837
1975	73.06824436879845
1976	70.54082530168141
1977	70.51538545653362
1978	71.44764057228412
1979	71.27189197729675
1980	71.45598338905056
1981	71.91836375209675
1982	72.24977392977394
1983	71.66528381260144
1984	71.71111924009213
1985	71.94021074233395
1986	73.50543303542725
1987	74.25115207373271
1988	72.71844177372566
1989	72.03897670617083
1990	82.8698553948832
1991	80.97502972651606
1992	81.04426787741204
1993	81.31041890440387
1994	81.11227701993704
1995	81.11455108359134
1996	82.20742150333015
1997	83.03571428571429
1998	81.13391984359725
1999	81.97621225983531
2000	81.92446043165468
2001	81.97009674582235
2002	81.23324396782841
2003	82.28995057660626
2004	82.74231678486997
2005	81.74409127954361
2006	80.6287170773152
2007	81.03025347506131
2008	79.67269595176572