Year	Percent
1991	20.501
1992	19.333
1993	17.899
1994	15.2
1995	16.112
1996	17.489
1997	22.409
1998	25.621
1999	18.774
2000	20.627
2001	22.572
2002	23.367
2003	24.224
2004	27.723
2005	28.76
2006	28.755
2007	28.787
2008	28.2
2009	17.868
2010	18.304
2011	18.531
2012	18.096
2013	18.65
2014	17.528
2015	17.866
2016	18.996
2017	18.951
2018	19.151
2019	19.218
2020	19.259
2021	19.319
2022	19.327