Year	Percent
1970	50.81081
1971	51.18734
1972	51.54639
1973	52.14106
1974	52.57985
1975	52.9976
1976	53.39578
1977	53.77574
1978	54.36242
1979	54.92341
1980	55.34188
1981	55.9499
1982	56.32653
1983	56.88623
1984	57.30994
1985	58.01527
1986	58.39552
1987	58.94161
1988	59.46429
1989	60.13986
1990	60.68376
1991	61.30653
1992	61.80328
1993	62.27929
1994	62.89308
1995	63.48228
1996	64.04834
1997	64.59259
1998	65.26163
1999	65.7632
2000	66.38655
2001	66.8956
2002	67.34143
2003	67.90451
2004	68.57888
2005	69.01408
2006	69.52141
2007	70.13631
2008	70.52375
2009	71.10312
2010	71.6647
2011	72.00929
2012	72.54005
2013	73.05524
2014	73.66667
2015	74.07002