Year	Percent
1960	19.97574
1961	20.66149
1962	21.37387
1963	22.11317
1964	22.88364
1965	23.38608
1966	23.89285
1967	24.41743
1968	24.97303
1969	25.56874
1970	26.21976
1971	26.92978
1972	27.69779
1973	28.50875
1974	28.88888
1975	29.05607
1976	29.21985
1977	29.37992
1978	29.54016
1979	29.70097
1980	29.86528
1981	30.02918
1982	30.19714
1983	30.37268
1984	30.56277
1985	30.76804
1986	30.93946
1987	31.10719
1988	31.29385
1989	31.49474
1990	31.71243
1991	31.9457
1992	32.19674
1993	32.46381
1994	32.74964
1995	33.05555
1996	33.38502
1997	33.73373
1998	34.10257
1999	34.48664
2000	34.88473
2001	35.29249
2002	35.71522
2003	36.15396
2004	36.61335
2005	37.08102
2006	37.48202
2007	37.90386
2008	38.34843
2009	38.81255
2010	39.30044
2011	39.81167
2012	40.34813
2013	40.90588
2014	41.48856
2015	42.09488
2016	42.72659
2017	43.3804