Year	Percent
1960	24.97041
1961	25.45519
1962	25.91517
1963	26.38254
1964	26.86221
1965	27.35189
1966	27.85905
1967	28.38272
1968	28.92454
1969	29.47749
1970	29.97047
1971	30.00944
1972	30.05646
1973	30.11155
1974	30.18304
1975	30.27272
1976	30.38243
1977	30.50727
1978	30.65033
1979	30.80897
1980	30.99473
1981	31.26489
1982	31.5517
1983	31.85332
1984	32.1702
1985	32.49776
1986	32.83979
1987	33.19451
1988	33.56257
1989	33.93871
1990	34.34382
1991	34.87086
1992	35.41381
1993	35.96597
1994	36.5313
1995	37.1072
1996	37.69515
1997	38.29112
1998	38.90372
1999	39.53561
2000	40.11699
2001	40.1922
2002	40.28045
2003	40.37924
2004	40.48788
2005	40.60151
2006	40.72408
2007	40.85495
2008	40.99409
2009	41.13673
2010	41.28579
2011	41.44003
2012	41.6009
2013	41.77084
2014	41.95369
2015	42.152
2016	42.36682
2017	42.59792