Year	Percent
1970	40.35936
1971	38.48229
1972	39.12901
1973	47.8462
1974	53.26742
1975	56.72646
1976	58.85424
1977	57.99074
1978	58.00948
1979	57.003
1980	58.44973
1981	59.25926
1982	61.63752
1983	63.46352
1984	63.8972
1985	64.59202
1986	65.27949
1987	63.56811
1988	67.11115
1989	65.17155
1990	66.00883
1991	63.66713
1992	64.34587
1993	62.83534
1994	63.9263
1995	66.12254
1996	63.38676
1997	64.9501
1998	65.45857
1999	63.09021
2000	63.17264
2001	60.02932
2002	64.30271
2003	63.43279
2004	65.37114
2005	68.75568
2006	68.30986
2007	70.54157
2009	71.36442
2010	76.48851
2011	75.89785
2012	77.17138
2013	77.49684
2014	77.69717
2015	81.4692