Year	Percent
1991	18.351
1992	18.699
1993	19.028
1994	19.541
1995	19.193
1996	20.166
1997	19.771
1998	19.842
1999	19.996
2000	20.162
2001	21.07
2002	21.531
2003	22.426
2004	21.872
2005	23.769
2006	22.755
2007	22.665
2008	22.138
2009	22.899
2010	23.562
2011	20.317
2012	17.796
2013	17.027
2014	16.841
2015	15.737
2016	15.648
2017	16.627
2018	17.589
2019	18.134
2020	18.28
2021	18.379
2022	18.313