Year	Percent
1971	27.01225
1972	29.6399
1973	29.21637
1975	31.74353
1988	37.5362
1989	35.40575
1990	35.06271
1991	33.7905
1992	31.00875
1993	31.90892
1994	29.14634
1995	28.91203
1996	29.4962
1998	30.22362
1999	33.51795
2000	36.70574
2001	36.19732
2002	36.25742
2003	40.09122
2004	45.97765
2005	58.28878
2006	57.07948
2007	61.22326
2008	67.43195
2009	73.94515
2010	70.37509
2011	70.69733
2012	69.12875
2013	67.96234
2014	68.19926
2015	68.65476
2016	67.57843