Year	% of total
1970	79.96979533525324
1971	77.6425686486036
1972	77.81485582672633
1973	79.07063588604471
1974	78.104947612943
1975	78.74042937276417
1976	79.4539322674585
1977	80.8707751830869
1978	79.81235387407418
1979	77.32373284243637
1980	76.66058242069643
1981	77.67967656413568
1982	78.65292473732849
1983	80.8306031932879
1984	80.13485874356547
1985	80.95327287380266
1986	81.57197109848832
1987	81.2428694799053
1988	81.69030989014654
1989	81.78910604230808
1990	85.33455545371218
1991	86.21533442088092
1992	85.40983606557377
1993	85.29874213836479
1994	86.80509042196918
1995	86.97421981004071
1996	88.37064676616916
1997	88.50063532401525
1998	89.93746446844798
1999	90.51580698835274
2000	91.20296767355592
2001	89.98842592592592
2002	90.03852504127683
2003	90.29927760577915
2004	90.32738095238095
2005	89.57688338493293
2006	89.03394255874673
2007	89.35342732134175
2008	87.29805013927576