Year	Percent
1960	21.87473
1961	21.51593
1962	21.4652
1963	20.13226
1964	25.79075
1965	24.81893
1966	23.97162
1967	24.00336
1968	28.72046
1969	29.62619
1970	32.88706
1971	32.18039
1972	33.14916
1973	30.98262
1974	26.16461
1975	32.78219
1976	36.13187
1977	43.07777
1978	43.91662
1979	33.19854
1980	26.39356
1981	24.42521
1982	27.68959
1983	12.2063
1984	18.12009
1985	19.14852
1986	20.81088
1987	25.18549
1988	27.88598
1989	12.70067
1990	10.21994
1991	18.67801
1992	23.72129
1993	18.75099
1994	14.15634
1995	18.11389
1996	16.55475
1997	27.67253
1998	30.6604
1999	26.51678
2000	24.17039
2001	27.52417
2002	21.15889
2003	15.21744
2004	21.79846
2005	23.00403
2006	26.92191
2007	30.34004
2008	26.82613
2009	25.79695
2010	21.97166
2011	23.0724
2012	26.59674
2013	27.26895
2014	24.8102