Year	Percent
1960	23.37559
1961	23.59701
1962	23.98449
1963	24.33642
1964	24.71832
1965	25.1329
1966	25.50166
1967	25.6729
1968	25.85114
1969	25.99482
1970	26.07433
1971	26.09221
1972	26.12849
1973	26.13286
1974	26.12405
1975	26.1182
1976	26.14852
1977	26.2183
1978	26.27185
1979	26.34834
1980	26.4736
1981	26.50915
1982	26.29319
1983	26.14072
1984	26.0124
1985	26.00383
1986	26.01135
1987	25.97797
1988	26.05853
1989	26.13118
1990	26.07834
1991	25.9442
1992	25.97317
1993	26.04905
1994	26.15309
1995	26.22643
1996	26.23132
1997	26.20003
1998	26.15859
1999	26.0952
2000	25.97881
2001	25.79535
2002	25.59521
2003	25.43655
2004	25.22889
2005	24.9347
2006	24.52663
2007	24.1183
2008	23.92016
2009	23.96677
2010	24.12721
2011	24.30835
2012	24.47051
2013	24.60768
2014	24.69547
2015	24.73062
2016	24.72068
2017	24.68872