Year	Percent
1991	21.719
1992	21.462
1993	21.004
1994	20.714
1995	20.141
1996	19.743
1997	19.229
1998	19.464
1999	18.863
2000	18.364
2001	17.974
2002	17.433
2003	16.955
2004	15.346
2005	16.096
2006	16.018
2007	16.062
2008	15.753
2009	13.368
2010	13.611
2011	11.253
2012	13.23
2013	14.218
2014	14.27
2015	13.746
2016	13.208
2017	13.114
2018	13.013
2019	12.895
2020	12.765
2021	12.628
2022	12.489