Year	Percent
1960	22.52899
1961	22.4747
1962	23.07057
1963	23.14438
1964	23.11169
1965	23.86715
1966	24.26994
1967	23.24475
1968	22.93899
1969	23.76704
1970	21.36307
1971	21.86502
1972	22.52185
1973	23.27997
1974	22.64229
1975	20.22886
1976	21.9891
1977	23.4795
1978	24.77937
1979	25.06538
1980	23.26809
1981	24.24743
1982	22.06233
1983	22.22794
1984	25.07658
1985	24.14507
1986	23.68612
1987	23.54755
1988	22.75734
1989	22.44966
1990	21.46999
1991	20.05875
1992	20.01939
1993	20.3339
1994	21.21641
1995	21.20499
1996	21.62923
1997	22.36307
1998	22.84841
1999	23.31795
2000	23.56893
2001	22.05149
2002	21.57652
2003	21.65997
2004	22.52673
2005	23.22295
2006	23.33301
2007	22.35135
2008	20.78624
2009	17.51293
2010	18.3946
2011	18.54476
2012	19.35061
2013	19.76226
2014	20.14481
2015	20.428
2016	19.68879