Year	Percent
1991	20.974
1992	20.715
1993	20.447
1994	19.819
1995	18.743
1996	17.755
1997	16.262
1998	16.012
1999	15.759
2000	14.939
2001	14.964
2002	14.863
2003	14.889
2004	14.271
2005	14.134
2006	13.988
2007	13.852
2008	13.749
2009	13.686
2010	14.178
2011	15.228
2012	17.8
2013	16.258
2014	17.477
2015	16.707
2016	14.228
2017	14.196
2018	14.132
2019	14.117
2020	14.127
2021	14.119
2022	14.104