Year	Percent
1960	6.01574
1961	7.39944
1962	8.79906
1963	9.8071
1964	12.28287
1965	13.2622
1966	21.81572
1967	25.4462
1968	30.73684
1969	38.25383
1970	45.3227
1971	50.44053
1972	50.94414
1973	50.89997
1974	47.87208
1975	41.89987
1976	33.77125
1977	33.46483
1978	36.36364
1979	37.2194
1980	40.05215
1981	43.40568
1982	37.65849
1983	29.38912
1984	29.44353
1985	22.99441
1986	21.48535
1987	15.50083
1988	23.58452
1989	36.10818
1990	37.36698
1991	33.21017
1992	30.4193
1993	28.77953
1994	25.98254
1995	27.13013
1996	23.44352
1997	24.05199
1998	37.93667
1999	25.62595
2000	29.55108
2001	29.88814
2002	30.19381
2003	30.14301
2004	31.4797
2005	27.15034
2006	25.9047
2007	30.79236
2008	36.18711
2009	38.93023
2010	41.41207
2011	37.76143
2012	38.13663
2013	29.40908
2014	27.85636
2015	32.07854
2016	24.30057