Year	Percent
1960	6.97382
1961	6.79412
1962	7.96386
1963	7.80459
1964	10.42302
1965	10.72302
1966	10.31509
1967	8.10283
1968	9.26235
1969	9.1864
1970	8.72908
1971	7.68384
1972	6.0641
1973	12.11034
1974	13.37273
1975	11.61105
1976	14.4492
1977	16.72907
1978	14.30971
1979	15.68645
1980	20.11668
1981	19.80597
1982	20.04288
1983	20.87162
1984	21.43055
1985	20.32166
1986	20.37901
1987	19.60082
1988	19.93621
1989	19.78671
1990	20.14563
1991	21.1195
1992	21.71789
1993	22.93426
1994	23.46999
1995	23.58082
1996	21.68392
1997	21.86267
1998	22.66074
1999	22.37587
2000	22.27938
2001	22.58381
2002	22.83925
2003	22.47415
2004	22.77972
2005	23.29984
2006	24.09532
2007	24.50054
2008	24.727
2009	25.29557
2010	24.95648
2011	25.0453
2012	25.30996
2013	26.30707
2014	26.31105
2015	26.83139
2016	27.34612
2017	27.7509