Year	Percent
1991	27.907
1992	28.602
1993	29.553
1994	29.977
1995	30.203
1996	30.353
1997	30.475
1998	30.44
1999	30.509
2000	30.419
2001	30.699
2002	30.822
2003	31.164
2004	29.325
2005	29.698
2006	29.861
2007	30.003
2008	30.471
2009	30.835
2010	30.657
2011	30.731
2012	30.965
2013	31.169
2014	31.541
2015	31.64
2016	31.604
2017	31.33
2018	30.97
2019	30.788
2020	30.646
2021	30.493
2022	30.379