Year	Percent
1960	10.96419
1961	10.18034
1962	11.14815
1963	12.80552
1964	12.08769
1965	11.23773
1966	11.49773
1967	13.4607
1968	13.09042
1969	14.01701
1970	14.00467
1971	16.10195
1972	11.64319
1973	8.71997
1974	11.61527
1975	8.05236
1976	6.25179
1977	6.04968
1978	8.28154
1979	6.5801
1980	6.15454
1981	5.60832
1982	9.093
1983	7.40961
1984	8.13984
1985	8.73202
1986	8.44692
1987	9.71822
1988	10.79235
1989	11.13623
1990	12.70408
1991	15.17127
1992	15.93893
1993	15.24579
1994	14.68183
1995	12.41203
1996	20.17269
1997	18.17856
1998	16.44715
1999	19.54912
2000	19.48382
2001	19.30206
2002	20.21742
2003	20.98414
2004	20.14569
2005	22.35515
2006	21.13037
2007	22.08306
2008	22.97777
2009	24.99741
2010	25.55596
2011	27.45723
2012	27.29713
2013	28.35081
2014	27.2817
2015	24.6164
2016	25.52021
2017	24.01175