Year	Percent
1960	15.12605
1961	13.93442
1962	13.6
1963	12.5
1964	18.46154
1965	21.50538
1966	26.50055
1967	21.33367
1968	21.67828
1969	20.06359
1970	24.51569
1971	24.9022
1972	21.92927
1973	23.06397
1974	30.68728
1975	24.55937
1976	29.26752
1977	28.73242
1978	28.66345
1979	27.9799
1980	25.1043
1981	25.94057
1982	26.78998
1983	27.03272
1984	26.64713
1985	25.00545
1986	27.66478
1987	21.59973
1988	19.95413
1989	17.50504
1990	15.60671
1991	20.87256
1992	17.44679
1993	20.18741
1994	36.75513
1995	22.41918
1996	23.00456
1997	20.7933
1998	17.3424
1999	17.21999
2000	15.15904
2001	21.91457
2002	18.65814
2003	17.44124
2004	18.28162
2005	23.0898
2006	23.43255
2007	24.76974
2008	29.6628
2009	28.69458
2010	29.93755
2011	38.1406
2012	39.40685
2013	39.42063
2014	39.82815
2015	37.03109
2016	38.23256
2017	34.49639