Year	Percent
1960	40.5782
1961	40.88972
1962	41.17158
1963	41.46699
1964	41.78028
1965	42.10842
1966	42.458
1967	42.82345
1968	43.19212
1969	43.54167
1970	43.86441
1971	43.96143
1972	43.96684
1973	43.95855
1974	43.96317
1975	43.99504
1976	44.06022
1977	44.14863
1978	44.25198
1979	44.35311
1980	44.44232
1981	44.37644
1982	44.2404
1983	44.10058
1984	43.96508
1985	43.83695
1986	43.71981
1987	43.61228
1988	43.51611
1989	43.42976
1990	43.35624
1991	43.28441
1992	43.15723
1993	43.04423
1994	42.9506
1995	42.87732
1996	42.8259
1997	42.79215
1998	42.77276
1999	42.76024
2000	42.75038
2001	42.73925
2002	42.78919
2003	42.87947
2004	42.97681
2005	43.08081
2006	43.19461
2007	43.31585
2008	43.44209
2009	43.56663
2010	43.68915
2011	43.63516
2012	43.49654
2013	43.35934
2014	43.22982
2015	43.11106
2016	43.00438
2017	42.90761