Year	Percent
1960	13.37589
1961	13.22778
1962	13.0622
1963	13.41078
1964	14.33291
1965	15.32031
1966	16.38555
1967	17.52418
1968	18.72801
1969	19.97131
1970	21.24769
1971	22.54677
1972	23.87517
1973	25.23248
1974	26.64478
1975	27.3451
1976	27.8698
1977	28.39253
1978	28.88556
1979	29.30278
1980	29.63245
1981	29.87351
1982	30.08075
1983	30.31884
1984	30.66466
1985	31.15477
1986	31.80436
1987	32.60041
1988	33.55062
1989	34.64744
1990	35.90404
1991	37.32058
1992	38.90681
1993	39.39749
1994	39.59259
1995	39.86995
1996	40.23309
1997	40.65944
1998	41.10179
1999	41.49269
2000	41.78996
2001	41.97095
2002	42.06
2003	42.09316
2004	42.12318
2005	42.5789
2006	43.19317
2007	43.84891
2008	44.12263
2009	44.37125
2010	44.58533
2011	44.75895
2012	44.91496
2013	45.09533
2014	45.35189
2015	45.7184
2016	46.20466
2017	46.79887