Year	Percent
1991	73.60508
1992	72.54674
1993	72.75646
1994	72.06157
1995	72.74378
1996	73.00994
1997	74.19493
1998	73.02494
1999	74.98502
2000	75.28324
2001	77.22227
2002	77.32377
2003	77.12853
2004	78.42389
2005	78.17847
2006	77.8805
2007	78.33338
2008	77.82163
2009	78.10229
2010	78.04402
2011	77.78908
2012	78.06209
2013	77.87917
2014	79.14913
2015	79.61719
2016	79.2944
2017	79.34035