Year	Percent
1991	30.583
1992	30.498
1993	30.349
1994	30.088
1995	29.86
1996	29.685
1997	29.514
1998	29.424
1999	29.339
2000	29.21
2001	29.076
2002	29.061
2003	29.033
2004	29.053
2005	29.14
2006	28.99
2007	28.699
2008	28.657
2009	28.615
2010	28.278
2011	28.608
2012	28.993
2013	29.367
2014	29.774
2015	30.186
2016	30.358
2017	30.779
2018	31.156
2019	31.52
2020	31.849
2021	32.132
2022	32.375