Year	Percent
1983	75.58199
1984	74.54882
1985	74.99071
1986	74.92686
1987	74.51331
1989	74.17766
1990	74.61296
1991	74.56741
1992	73.54285
1993	73.95745
1994	73.82428
1995	73.1523
1996	73.04226
1997	73.35146
1998	73.35502
1999	73.63293
2000	73.66063
2001	73.92201
2002	74.23468
2003	74.28732
2004	73.34065
2005	74.51394
2006	74.71513
2007	74.95727
2008	75.6161
2009	76.12377
2010	75.8168
2011	75.98451
2012	76.05823
2013	76.13332
2014	76.27495
2015	76.58491
2016	77.04435
2017	77.755