Year	Percent
1960	30.191
1961	31.112
1962	32.074
1963	33.052
1964	34.046
1965	35.052
1966	36.073
1967	37.106
1968	38.153
1969	39.207
1970	40.274
1971	41.351
1972	42.437
1973	43.527
1974	44.626
1975	45.729
1976	46.838
1977	47.948
1978	49.061
1979	50.175
1980	51.29
1981	52.401
1982	53.05
1983	53.323
1984	53.596
1985	53.868
1986	54.14
1987	54.412
1988	54.684
1989	54.955
1990	55.226
1991	55.497
1992	55.767
1993	56.037
1994	56.752
1995	57.598
1996	58.441
1997	59.276
1998	60.107
1999	60.933
2000	61.753
2001	62.565
2002	63.371
2003	64.605
2004	66.003
2005	67.37
2006	68.71
2007	70.02
2008	71.3
2009	72.542
2010	73.753
2011	74.827
2012	75.802
2013	76.749
2014	77.67
2015	78.566
2016	79.436
2017	80.277