Year	Percent
1970	54.41527
1971	55.11628
1972	56.00907
1973	56.73289
1974	57.5431
1975	58.40336
1976	59.1002
1977	59.88024
1978	60.89494
1979	61.66983
1980	62.59259
1981	63.53791
1982	64.43662
1983	65.46392
1984	66.61074
1985	67.70492
1986	68.64
1987	69.95305
1988	71.10092
1989	72.19731
1990	73.39181
1991	74.53505
1992	75.77031
1993	77.09191
1994	78.22581
1995	79.44664
1996	80.41505
1997	81.25
1998	81.93225
1999	82.81829
2000	83.45499
2001	84.17266
2002	84.76978
2003	85.33178
2004	85.99311
2005	86.42534
2006	86.94196
2007	87.44493
2008	87.83931
2009	88.31726
2010	88.68922
2011	89.14405
2012	89.49537
2013	89.92879
2014	90.26104
2015	90.58474