Year	Percent
1991	82.94513
1992	83.09046
1993	83.04123
1994	83.3256
1995	83.2935
1996	83.18828
1997	83.30121
1998	83.27832
1999	83.23579
2000	83.18573
2001	83.10683
2002	82.98532
2003	82.84955
2004	82.72537
2005	82.58825
2006	82.46988
2007	82.30131
2008	82.15851
2009	82.00822
2010	81.85149
2011	81.68973
2012	81.58459
2013	81.44058
2014	81.26698
2015	81.03307
2016	80.82728
2017	80.70247
2018	80.49796
2019	80.29374