Year	Percent
1991	31.923
1992	31.565
1993	31.115
1994	30.77
1995	30.738
1996	30.482
1997	30.219
1998	30.13
1999	29.999
2000	29.663
2001	29.883
2002	29.97
2003	30.03
2004	29.965
2005	30.029
2006	30.133
2007	30.206
2008	30.238
2009	30.184
2010	29.947
2011	29.764
2012	29.505
2013	29.167
2014	28.807
2015	28.413
2016	28.066
2017	28.054
2018	28.064
2019	28.083
2020	28.106
2021	28.135
2022	28.168