Year	Percent
1991	30.979
1992	30.274
1993	29.93
1994	28.823
1995	28.944
1996	30.082
1997	31.346
1998	30.507
1999	29.077
2000	28.411
2001	27.02
2002	26.528
2003	27.635
2004	28.983
2005	26.452
2006	26.027
2007	25.944
2008	27.111
2009	25.375
2010	23.712
2011	25.181
2012	23.897
2013	22.624
2014	21.553
2015	20.659
2016	19.694
2017	19.393
2018	19.17
2019	18.914
2020	18.542
2021	18.246
2022	17.951