Year	Percent
1960	27.09707
1961	28.67275
1962	29.17037
1963	28.87275
1964	26.82272
1965	25.81512
1966	24.33774
1967	24.2941
1968	22.36965
1969	21.33099
1970	20.92049
1971	22.40607
1972	20.44202
1973	25.08667
1974	38.66463
1975	28.82819
1976	25.80849
1977	23.21619
1978	20.4072
1979	25.96038
1980	28.77772
1981	26.84385
1982	22.16344
1983	19.51291
1984	26.81108
1985	24.11814
1986	19.81724
1987	21.43827
1988	20.56868
1989	34.12343
1990	39.45002
1991	31.35327
1992	26.35301
1993	26.95834
1994	30.86333
1995	27.10715
1996	36.51415
1997	29.25901
1998	20.92049
1999	22.91171
2000	29.74422
2001	22.73563
2002	30.43357
2003	33.85339
2004	36.19835
2005	39.65865
2006	36.51862
2007	31.13054
2008	30.82167
2009	18.07152
2010	28.53041
2011	29.94301
2012	26.17101
2013	24.76498
2014	16.69383