Year	Percent
1960	14.28572
1961	12.31527
1962	13.11475
1963	11.73792
1964	9.97124
1965	16.98167
1966	18.13296
1967	19.06929
1968	20.54771
1969	17.54132
1970	19.24093
1971	19.14237
1972	23.34292
1973	20.08948
1974	21.45312
1975	22.20543
1976	26.40848
1977	29.9321
1978	27.47618
1979	32.77407
1980	25.33361
1981	24.35383
1982	29.7072
1983	24.19371
1984	29.27638
1985	26.17438
1986	29.62407
1987	26.77941
1988	31.13442
1989	23.78977
1990	27.02938
1991	29.55289
1992	27.05354
1993	28.12602
1994	37.18796
1995	33.88548
1996	19.10167
1997	21.27668
1998	24.95047
1999	21.28509
2000	22.74591
2001	20.28525
2002	19.3127
2003	24.76019
2004	24.37905
2005	29.28993
2006	38.40987
2007	27.87015
2008	28.5504
2009	26.99288
2010	30.09525
2011	37.17769
2012	35.77881
2013	33.35487
2014	29.13235
2015	27.49185
2016	24.11654
2017	27.78711