Year	Percent
1991	11.441
1992	10.678
1993	10.601
1994	10.234
1995	12.393
1996	13.698
1997	12.788
1998	13.703
1999	13.535
2000	13.065
2001	13.041
2002	13.187
2003	13.522
2004	13.475
2005	13.56
2006	13.806
2007	13.971
2008	14.091
2009	14.161
2010	13.857
2011	14.836
2012	15.434
2013	15.857
2014	16.411
2015	16.808
2016	17.234
2017	17.147
2018	17.668
2019	17.996
2020	18.124
2021	18.239
2022	18.348