Year	Percent
1960	11.96612
1961	12.76233
1962	13.23578
1963	12.85301
1964	13.44691
1965	13.85697
1966	13.97725
1967	14.92091
1968	14.16763
1969	15.68051
1970	15.45458
1971	15.82102
1972	15.21533
1973	15.04823
1974	17.86936
1975	17.21998
1976	15.86193
1977	16.79117
1978	17.4464
1979	17.40942
1980	17.87199
1981	17.34687
1982	18.41162
1983	18.94026
1984	19.02252
1985	18.24249
1986	17.77324
1987	17.90073
1988	19.11245
1989	18.99842
1990	19.92518
1991	19.83869
1992	21.6703
1993	21.28979
1994	21.8308
1995	21.43827
1996	21.76776
1997	20.95764
1998	21.15709
1999	20.66497
2000	20.4627
2001	21.65116
2002	22.33775
2003	21.4378
2004	21.72747
2005	20.54085
2006	20.66872
2007	20.80416
2008	20.11498
2009	20.53451
2010	20.45554
2011	21.54687
2012	21.39453
2013	20.80083
2014	20.86835
2015	20.79364
2016	20.26493
2017	20.51787