Year	Percent
1991	73.44004
1992	73.33129
1993	73.15901
1994	72.99435
1995	72.7908
1996	72.56566
1997	72.28537
1998	72.0249
1999	71.69996
2000	71.41406
2001	70.99083
2002	70.45042
2003	70.06817
2004	69.68422
2005	69.25502
2006	68.93171
2007	68.27835
2008	67.76535
2009	67.58582
2010	67.03023
2011	66.38489
2012	65.69516
2013	65.11756
2014	64.55387
2015	63.97985
2016	62.98965
2017	62.0273
2018	61.32072
2019	60.65024