Year	Percent
1979	82.40337
1980	83.22618
1981	83.64651
1982	82.82776
1983	82.43079
1984	81.59341
1985	81.23796
1986	81.49815
1987	81.48169
1988	81.94554
1989	82.13428
1991	82.89269
1992	82.53753
1993	82.15331
1994	82.34685
1995	84.56808
1996	80.73134
1997	82.30915
1998	81.3103
1999	80.29529
2001	80.49806
2002	80.85221
2003	81.17873
2004	80.16633
2006	81.24457
2007	80.71071
2008	81.00797
2011	81.40865
2012	81.06493
2013	81.51974
2014	81.61929
2015	82.02765