Year	Percent
1979	72.17631
1980	72.83486
1981	73.48125
1982	73.35748
1983	74.04086
1984	74.55796
1985	75.14563
1986	75.75323
1987	75.36436
1988	75.93951
1989	76.98448
1990	78.45756
1991	79.63195
1992	80.69164
1993	81.96385
1994	82.64429
1995	83.10838
1996	83.96265
1997	84.23783
1998	84.34748
1999	84.64329
2000	85.4326
2001	86.27057
2002	86.86664
2003	87.33306
2005	87.98727
2008	89.69436
2009	89.96458
2010	90.24677
2011	90.95536
2012	91.17532
2013	91.26771
2014	92.87365
2015	91.86352
2016	92.23408
2017	92.32432