Year	Percent
1970	43.73494
1971	45.64391
1972	45.7366
1973	47.52629
1974	48.62954
1975	48.86442
1976	50.00066
1977	51.51378
1978	52.19973
1980	54.44901
1981	57.47164
1982	59.95932
1983	62.59406
1984	64.36257
1985	66.22836
1986	64.71653
1987	64.93025
1988	64.36663
1989	64.17452
1990	65.36741
1991	68.97991
1992	72.85135
1993	76.43573
1994	76.55666
1995	78.41967
1996	82.51583
1998	92.52771
1999	89.36188
2000	92.22491
2001	92.28853
2002	93.97759
2003	96.4428
2004	95.15802
2005	95.43834
2006	94.16052
2007	94.66296
2008	94.27292
2009	93.82156
2010	92.4227
2011	89.68628
2012	89.08832