Year	Percent
1971	10.05257
1972	9.23434
1973	9.6107
1974	10.36502
1976	11.50674
1977	13.81914
1978	12.93356
1979	13.63453
1980	12.0615
1981	11.61676
1983	11.82883
1984	11.301
1985	10.66622
1986	9.79564
1987	9.73041
1988	9.40735
2000	31.02327
2001	35.06623
2002	35.95749
2003	38.97694
2004	40.76734
2005	42.1615
2006	47.19997
2007	50.17939
2008	52.8127
2009	54.36558
2010	57.4676
2011	58.17671
2012	54.46881
2013	54.17443
2014	53.13399
2015	50.86188
2016	50.98531