Year	Percent
1960	19.67428
1961	13.8695
1962	7.59442
1963	6.92646
1964	6.88438
1965	7.89792
1966	8.83974
1967	14.41401
1968	16.61508
1969	21.15079
1970	19.4616
1971	10.8796
1972	12.59446
1973	19.12388
1974	27.93353
1975	11.79876
1976	12.79095
1977	11.10324
1978	8.41503
1979	11.42066
1980	6.88928
1981	4.76222
1982	6.08432
1983	7.84266
1984	10.13921
1985	13.78749
1986	13.10688
1987	8.73804
1988	10.34624
1989	13.7316
1990	12.73257
1991	11.70034
1992	15.64657
1993	17.26999
1994	19.41136
1995	20.33548
1996	22.61638
1997	21.11174
1998	19.46698
1999	22.4423
2000	25.01885
2001	23.53448
2002	25.08607
2003	23.6994
2004	24.86308
2005	25.57984
2006	31.89552
2007	33.27115
2008	30.66193
2009	32.16621
2010	32.88478
2011	32.5297
2012	31.02659
2013	32.01523
2014	34.16929
2015	35.23478
2016	35.10445
2017	36.04661