Year	% of total
1970	78.24524602332882
1971	78.13232791589516
1972	78.45533963238232
1973	78.4770557004188
1974	78.44591377621049
1975	78.49608976286335
1976	78.50240908211005
1977	78.41990062199675
1978	78.531167448565
1979	78.0625451771417
1980	77.4316078951493
1981	76.52965703506564
1982	75.86408923476881
1983	75.81308477405308
1984	74.20062007231726
1985	72.89223520653036
1986	71.6846569295983
1987	70.37767284959455
1988	69.49013549311127
1989	68.94258258316471
1990	77.313769751693
1991	76.83741648106904
1992	76.81159420289855
1993	76.83863885839737
1994	76.33928571428571
1995	75.85825027685493
1996	75.19294377067254
1997	75.55803571428571
1998	76.20111731843575
1999	74.71395881006865
2000	75.72254335260115
2001	75.70303712035995
2002	76.1574074074074
2003	75.78947368421053
2004	76.5625
2005	77.02702702702703
2006	76.68329177057358
2007	77.95765877957659
2008	78.07692307692308