Year	Percent
1960	9.24153
1961	9.18513
1962	8.26914
1963	8.77917
1964	9.20213
1965	10.89345
1966	10.41383
1967	11.07733
1968	9.92732
1969	11.39107
1970	8.40707
1971	10.83428
1972	10.96813
1973	15.91792
1974	25.17853
1975	18.33875
1976	18.21582
1977	24.87241
1978	19.5526
1979	24.81614
1980	29.37517
1981	22.18752
1982	17.83384
1983	14.53616
1984	15.70543
1985	17.3852
1986	13.31603
1987	26.94186
1988	22.85462
1989	43.98132
1990	35.34425
1991	41.70108
1992	37.50938
1993	33.82986
1994	24.31023
1995	35.76149
1996	32.23857
1997	41.7746
1998	29.69152
1999	33.86953
2000	51.73036
2001	45.44807
2002	35.96569
2003	39.7879
2004	30.16075
2005	31.65697
2006	43.11133
2007	33.72852
2008	39.88313
2009	30.76862
2010	25.26412
2011	31.32981
2012	31.43875
2013	18.04991
2014	18.43513
2015	10.66631
2016	9.21811