Year	Percent
1991	81.47093
1992	81.49818
1993	81.37538
1994	81.43241
1995	81.18331
1996	81.0296
1997	80.93282
1998	80.82795
1999	80.75642
2000	80.71949
2001	80.90985
2002	80.83577
2003	80.58367
2004	80.38292
2005	80.22362
2006	79.95147
2007	79.51153
2008	79.20234
2009	78.83785
2010	78.50231
2011	78.22549
2012	78.07815
2013	77.79354
2014	77.48601
2015	77.28818
2016	77.105
2017	76.8553
2018	76.63208
2019	76.37344