Year	Percent
1960	11.94735
1961	12.59243
1962	16.94768
1963	18.61724
1964	18.18492
1965	19.38365
1966	20.44779
1967	19.96482
1968	16.90297
1969	14.72688
1970	21.57647
1971	20.45416
1972	19.68046
1973	24.76697
1974	25.02111
1975	21.01806
1976	19.32694
1977	21.05864
1978	20.66739
1979	21.56087
1980	23.57261
1981	23.83379
1982	20.33439
1983	21.33972
1984	24.02413
1985	24.01558
1986	26.3282
1987	26.64215
1988	28.39278
1989	28.11202
1990	27.51623
1991	29.59726
1992	29.12977
1993	31.35961
1994	33.82569
1995	36.35728
1996	40.50666
1997	48.95648
1998	44.76423
1999	45.48931
2000	51.36929
2001	46.02685
2002	46.747
2003	47.15706
2004	48.57265
2005	46.13699
2006	46.57806
2007	43.2608
2008	36.91204
2009	32.23235
2010	34.80329
2011	32.03085
2012	30.81905
2013	28.01768
2014	28.91272
2015	28.39572
2016	27.96659
2017	30.55041