Year	Percent
1960	8.36673
1961	7.97236
1962	8.30365
1963	7.71229
1964	8.81176
1965	8.19316
1966	8.89285
1967	8.55112
1968	10.56861
1969	11.33291
1970	12.1888
1971	13.07585
1972	13.40306
1973	13.38541
1974	13.24789
1975	12.43519
1976	12.62717
1977	13.31542
1978	13.94614
1979	13.76991
1980	14.35936
1981	16.36158
1982	17.05857
1983	19.16684
1984	21.40527
1985	20.96485
1986	18.28464
1987	17.80989
1988	17.38581
1989	16.68204
1990	15.80025
1991	15.83634
1992	16.26522
1993	17.79386
1994	20.40859
1995	21.93183
1996	23.11841
1997	25.75374
1998	26.18321
1999	26.39724
2000	28.61617
2001	27.86222
2002	26.47714
2003	25.44731
2004	25.17889
2005	24.66778
2006	24.87197
2007	25.70774
2008	25.31649
2009	22.67342
2010	25.5193
2011	28.92011
2012	30.69998
2013	32.21753
2014	32.71299
2015	32.94006
2016	32.9466
2017	34.0928