Year	Percent
1991	18.299
1992	18.18
1993	19.114
1994	19.367
1995	20.054
1996	19.545
1997	20.125
1998	19.614
1999	20.034
2000	20.23
2001	19.41
2002	19.202
2003	19.835
2004	18.793
2005	18.201
2006	17.953
2007	18.005
2008	18.157
2009	17.243
2010	17.928
2011	17.489
2012	17.347
2013	17.361
2014	17.227
2015	16.447
2016	16.872
2017	16.928
2018	16.847
2019	16.8
2020	16.757
2021	16.708
2022	16.66