Year	Percent
1960	9.94881
1961	9.48575
1962	9.0514
1963	8.58751
1964	8.21921
1965	7.7009
1966	11.91864
1967	8.86612
1968	8.26871
1969	7.01761
1970	6.73943
1971	6.7118
1972	6.62486
1973	7.263
1974	9.22855
1975	11.04968
1976	11.0647
1977	10.86609
1978	10.72985
1979	11.6816
1980	12.75567
1981	12.42107
1982	12.19162
1983	10.7773
1984	12.05715
1985	10.92715
1986	10.1032
1987	10.16049
1988	11.09719
1989	12.45527
1990	13.11947
1991	14.32446
1992	15.19426
1993	16.09752
1994	16.06176
1995	18.38014
1996	18.32733
1997	18.62935
1998	18.38136
1999	18.25624
2000	20.31865
2001	19.57406
2002	20.81745
2003	21.93498
2004	25.21464
2005	29.97721
2006	32.62114
2007	31.5981
2008	43.46085
2009	31.88293
2010	34.80492
2011	42.09251
2012	43.0349
2013	42.0227
2014	38.52644
2015	31.4076
2016	27.49729
2017	28.70528