Year	Percent
1991	20.111
1992	19.668
1993	18.903
1994	18.417
1995	18.377
1996	17.907
1997	17.978
1998	18.153
1999	17.675
2000	17.416
2001	17.585
2002	17.351
2003	17.163
2004	17.348
2005	17.299
2006	18.692
2007	16.918
2008	15.854
2009	16.244
2010	16.784
2011	16.889
2012	17.225
2013	16.383
2014	15.951
2015	16.566
2016	17.288
2017	17.079
2018	17.075
2019	17.069
2020	17.062
2021	17.053
2022	17.044