Year	Percent
1960	11.33782
1961	11.53139
1962	15.47346
1963	17.3481
1964	19.81798
1965	21.71887
1966	21.74198
1967	21.94298
1968	24.64755
1969	28.30252
1970	38.19775
1971	40.1106
1972	40.88773
1973	38.93846
1974	44.53926
1975	38.80536
1976	39.59632
1977	35.24274
1978	37.86169
1979	42.12197
1980	45.03352
1981	44.78904
1982	46.28052
1983	46.46877
1984	46.95434
1985	41.1335
1986	36.58709
1987	36.5514
1988	33.44759
1989	34.10176
1990	35.64042
1991	33.96879
1992	35.49236
1993	37.17072
1994	32.86529
1995	33.84066
1996	35.02151
1997	38.20378
1998	31.56909
1999	32.70327
2000	34.89862
2001	27.76031
2002	25.47964
2003	17.66186
2004	23.1235
2005	21.3889
2006	22.34918
2007	23.16466
2008	30.53408
2009	27.79034
2010	28.23799
2011	27.1207
2012	29.89931
2013	30.67502
2014	30.15318
2015	27.12338
2016	27.02954
2017	27.64001