Year	Percent
1970	42.16934
1972	44.71365
1973	46.41201
1974	47.73182
1975	48.50382
1976	49.69157
1977	50.92839
1978	51.69437
1980	53.7782
1981	56.94761
1982	58.72086
1983	61.47347
1984	63.3937
1985	65.17872
1986	64.10611
1987	64.39471
1988	63.84486
1989	64.0954
1990	65.29739
1991	69.74745
1992	73.75739
1993	77.91904
1994	77.59635
1995	79.63603
1996	83.37135
1998	94.00303
1999	91.0157
2000	92.92936
2001	93.40362
2002	94.5419
2003	97.00376
2004	96.0472
2005	96.51559
2006	94.82463
2007	95.62821
2008	95.24761
2009	95.26069
2010	93.11008
2011	90.24646
2012	89.57017