Year	Percent
1983	74.11233
1984	73.32527
1985	73.5103
1986	73.29334
1987	72.9392
1988	72.25475
1989	72.05534
1990	72.31595
1991	72.22969
1992	71.33803
1993	71.46499
1994	71.28256
1995	70.44994
1996	70.00743
1997	70.23781
1998	69.97974
1999	70.35262
2000	69.99621
2001	70.07774
2002	70.42577
2003	70.3821
2004	69.67294
2005	70.58858
2006	70.8498
2007	70.96004
2008	71.52357
2009	71.7938
2010	71.27223
2011	71.37081
2012	71.47528
2013	71.4748
2014	71.81792
2015	72.28141
2016	72.86861
2017	73.30903