Year	Percent
1960	5.69087
1961	7.06903
1962	8.82138
1963	7.25497
1964	9.03593
1965	9.35468
1966	11.35703
1967	12.14408
1968	10.96877
1969	11.58831
1970	13.85633
1971	13.36756
1972	16.18412
1973	15.56501
1974	14.56675
1975	18.27544
1976	24.46282
1977	27.6647
1978	33.1177
1979	43.08085
1980	46.24233
1981	44.45175
1982	39.55171
1983	34.55161
1984	37.43388
1985	43.59351
1986	35.97506
1987	27.89961
1988	29.64449
1989	27.84957
1990	27.0088
1991	28.43659
1992	34.62705
1993	41.2055
1994	35.37599
1995	35.19773
1996	38.88778
1997	35.00217
1998	38.76273
1999	34.55704
2000	37.71395
2001	35.16734
2002	34.41633
2003	35.65916
2004	38.88108
2005	42.05414
2006	39.95214
2007	42.22437
2008	48.23727
2009	59.29086
2010	63.40498
2011	53.6731
2012	48.25553
2013	47.0267
2014	44.19127
2015	42.24496
2016	36.11282
2017	35.65274