Year	Percent
1991	17.766
1992	17.641
1993	17.729
1994	17.899
1995	18.12
1996	18.233
1997	18.526
1998	18.423
1999	19.196
2000	18.87
2001	18.829
2002	18.919
2003	18.54
2004	19.365
2005	20.06
2006	20.208
2007	20.845
2008	20.146
2009	19.428
2010	17.267
2011	17.987
2012	18.824
2013	19.464
2014	19.834
2015	20.427
2016	20.357
2017	20.468
2018	20.612
2019	20.78
2020	20.95
2021	21.109
2022	21.265