Year	Percent
1971	37.5886
1972	44.92971
1976	62.75559
1978	74.08159
1979	71.94923
1980	73.78928
1981	69.12992
1982	64.92519
1983	63.35427
1984	55.33715
1985	47.97592
1986	46.97933
1987	45.34305
1988	51.29182
1989	42.2278
1990	49.92045
1991	49.59908
1992	50.36622
1994	38.35532
1995	54.75047
1996	63.76454
1999	72.76542
2000	82.1468
2001	88.80495
2003	86.23043
2004	87.37226
2005	86.42196
2006	85.74675
2008	77.3268
2009	75.90771
2010	79.74774
2011	81.03498
2012	83.39616
2013	84.90294
2014	89.92623
2015	87.20444