Year	Percent
1991	18.069
1992	18.244
1993	19.066
1994	19.218
1995	19.198
1996	17.826
1997	18.402
1998	17.855
1999	18.006
2000	18.033
2001	17.179
2002	16.968
2003	17.528
2004	16.245
2005	16.041
2006	15.943
2007	16.172
2008	15.9
2009	15.271
2010	15.748
2011	15.425
2012	15.327
2013	15.353
2014	15.292
2015	14.891
2016	15.083
2017	15.204
2018	15.11
2019	15.057
2020	15.005
2021	14.946
2022	14.886