Year	Percent
1960	31.41588
1961	31.14957
1962	30.73217
1963	30.35141
1964	30.00522
1965	29.66632
1966	29.35841
1967	29.05801
1968	28.77598
1969	28.51791
1970	28.26738
1971	28.00152
1972	27.70398
1973	27.45098
1974	27.23625
1975	27.04307
1976	26.8564
1977	26.67455
1978	26.48433
1979	26.27409
1980	26.05827
1981	25.91436
1982	25.92751
1983	25.92284
1984	25.88633
1985	25.83242
1986	25.77774
1987	25.72836
1988	25.67698
1989	25.61619
1990	25.546
1991	25.54022
1992	25.55924
1993	25.58625
1994	25.61
1995	25.63159
1996	25.65624
1997	25.6803
1998	25.69618
1999	25.70164
2000	25.70147
2001	25.70809
2002	25.76059
2003	25.80234
2004	25.81776
2005	25.80242
2006	25.77488
2007	25.85986
2008	25.94399
2009	26.03621
2010	26.12261
2011	26.20965
2012	26.29888
2013	26.39493
2014	26.46999
2015	26.53469
2016	26.62194
2017	26.72749