Year	Percent
1991	18.195
1992	17.509
1993	16.543
1994	16.996
1995	17.31
1996	18.707
1997	18.444
1998	18.371
1999	17.897
2000	18.826
2001	18.755
2002	18.694
2003	18.843
2004	19.057
2005	19.431
2006	20.849
2007	21.079
2008	20.573
2009	20.61
2010	20.552
2011	20.805
2012	20.608
2013	20.525
2014	20.529
2015	20.282
2016	20.018
2017	20.097
2018	20.195
2019	20.289
2020	20.379
2021	20.45
2022	20.554