Year	Percent
1963	22.85992
1964	23.65108
1965	22.68836
1966	22.47285
1967	23.08869
1968	22.70233
1969	21.15505
1970	20.75078
1971	18.78244
1972	20.05358
1973	19.68666
1974	20.22222
1975	20.44808
1976	20.52928
1977	18.99713
1978	17.95785
1979	19.70195
1980	20.15858
1981	19.18197
1982	19.54217
1983	17.81255
1984	16.96064
1985	17.44246
1986	18.22193
1987	19.25225
1988	19.573
1989	21.36644
1990	21.08781
1991	21.45225
1992	21.96808
1993	22.2688
1994	21.96856
1995	20.81919
1996	20.7664
1997	21.31256
1998	20.91321
1999	18.96845
2000	19.51907
2001	20.52946
2002	19.79896
2003	18.53111
2004	19.62086
2005	16.30736
2006	16.0242
2007	15.35928
2008	16.08609
2009	16.67781
2010	16.97258
2011	17.41301
2012	16.72267
2013	16.33831
2014	15.11058
2015	14.91576
2016	14.34737