Year	Percent
1991	21.582
1992	19.93
1993	19.456
1994	18.145
1995	17.717
1996	16.721
1997	15.685
1998	14.967
1999	15.114
2000	15.125
2001	15.184
2002	15.084
2003	15.6
2004	15.828
2005	16.378
2006	16.529
2007	16.699
2008	17.447
2009	17.09
2010	17.029
2011	17.331
2012	17.256
2013	17.295
2014	17.011
2015	16.885
2016	17.194
2017	17.159
2018	17.204
2019	17.254
2020	17.292
2021	17.304
2022	17.321