Year	Percent
1991	30.742
1992	30.887
1993	30.856
1994	30.916
1995	30.847
1996	29.284
1997	29.338
1998	29.234
1999	29.163
2000	29.098
2001	29.085
2002	29.068
2003	29.084
2004	29.218
2005	29.266
2006	29.378
2007	29.563
2008	29.678
2009	29.794
2010	29.971
2011	30.142
2012	30.33
2013	30.514
2014	30.678
2015	30.784
2016	31.078
2017	31.247
2018	31.31
2019	31.281
2020	31.163
2021	30.963
2022	30.678