Year	Percent
1970	29.84614
1971	29.36799
1972	29.16788
1973	30.85519
1974	35.84829
1975	33.77922
1976	36.80715
1977	36.69682
1978	35.8165
1979	37.75012
1980	40.23068
1981	42.63475
1982	42.88141
1983	41.97802
1984	44.9573
1985	46.9222
1986	41.65765
1987	40.42561
1988	41.10445
1989	43.83614
1990	44.01134
1991	42.57813
1992	39.50114
1993	34.93776
1994	36.64259
1995	38.09714
1996	39.29227
1997	43.20668
1998	45.25742
1999	46.2548
2000	53.79651
2001	54.22629
2002	53.20062
2003	54.12277
2004	57.66184
2005	61.08831
2006	67.10496
2007	69.07642
2008	70.12212
2009	59.87082
2010	67.71067
2011	72.62037
2012	72.12122
2013	69.98775
2014	69.4403
2015	70.45114
2016	68.72378
2017	71.11844