Year	Percent
1960	19.48822
1961	20.4542
1962	20.55385
1963	18.90971
1964	20.06627
1965	10.29048
1966	11.11437
1967	12.03159
1968	13.91821
1969	12.10236
1970	13.01003
1971	16.69011
1972	15.55008
1973	16.6596
1974	18.75232
1975	19.33416
1976	17.97827
1977	18.13933
1978	18.56385
1979	18.1715
1980	17.87698
1981	15.29743
1982	17.75645
1983	15.3164
1984	15.68188
1985	16.03594
1986	17.4812
1987	22.36464
1988	23.65645
1989	24.82993
1990	21.83054
1991	21.52206
1992	20.6728
1993	23.13538
1994	23.49793
1995	24.62437
1996	21.94242
1997	23.48226
1998	25.50316
1999	22.82371
2000	27.33716
2001	27.52231
2002	27.88418
2003	24.64323
2004	26.11089
2005	28.48166
2006	29.37671
2007	30.65537
2008	33.89331
2009	26.85574
2010	32.40828
2011	33.36904
2012	31.5863
2013	30.96787
2014	29.65631
2015	23.98566
2016	19.14986
2017	21.28078