Year	Percent
1960	10.51873
1961	12.69683
1962	14.07561
1963	18.78797
1964	15.41395
1965	14.76451
1966	21.70058
1967	22.20657
1968	27.10507
1969	29.94358
1970	26.3382
1971	25.5585
1972	21.40476
1973	25.87286
1974	32.53341
1975	28.95927
1976	27.55599
1977	30.63071
1978	34.53249
1979	38.13259
1980	34.45567
1981	32.44567
1982	32.20867
1983	32.78249
1984	32.24829
1985	32.56594
1986	32.42217
1987	33.08975
1988	34.70419
1989	37.09622
1990	39.616
1991	41.37406
1992	38.4852
1993	37.47954
1994	38.53913
1995	39.00329
1996	39.68096
1997	37.42468
1998	27.7619
1999	30.9163
2000	32.94171
2001	31.55959
2002	30.93958
2003	32.01491
2004	32.11707
2005	32.16306
2006	32.70069
2007	32.57953
2008	33.0185
2009	28.46566
2010	32.02288
2011	32.95883
2012	31.00123
2013	29.10222
2014	29.27691
2015	28.91811
2016	29.25239
2017	31.07565