Year	Percent
1970	44.2109
1971	42.64125
1972	44.01609
1973	51.25081
1974	55.3798
1975	56.20097
1976	56.23719
1977	56.51743
1978	54.16781
1979	53.63253
1980	52.40994
1981	57.67998
1982	57.75305
1983	59.97916
1984	59.16388
1985	59.51565
1986	61.23508
1987	61.426
1988	62.29066
1989	58.72942
1990	59.37722
1991	57.65579
1992	56.54459
1993	58.59878
1994	59.66692
1995	60.7377
1996	58.7847
1997	58.93944
1998	61.7486
1999	57.98357
2000	60.00506
2001	58.18262
2002	60.13634
2003	57.26545
2004	60.72597
2005	63.49532
2006	64.99806
2007	76.09246
2009	71.65442
2010	74.55528
2011	74.97518
2012	74.59603
2013	76.71432
2014	74.30349
2015	79.71272