Year	Percent
1971	30.59756
1972	33.70193
1973	31.80347
1975	34.24165
1988	35.64789
1989	34.5285
1990	34.34947
1991	32.9802
1992	30.96381
1993	31.5313
1994	28.35873
1995	29.22484
1996	28.79596
1998	30.07042
1999	33.16755
2000	36.54815
2001	35.69924
2002	35.88312
2003	39.72098
2004	45.35966
2005	58.44003
2006	57.29302
2007	61.55154
2008	67.52905
2009	73.72885
2010	69.71221
2011	69.76233
2012	67.80203
2013	66.2512
2014	66.23316
2015	66.58794
2016	65.4186