Year	Percent
1991	41.005
1992	40.7
1993	39.842
1994	39.595
1995	39.574
1996	39.36
1997	38.545
1998	38.988
1999	38.832
2000	38.344
2001	38.517
2002	38.549
2003	39.053
2004	39.198
2005	39.197
2006	38.703
2007	39.027
2008	39.057
2009	38.869
2010	38.406
2011	37.892
2012	37.212
2013	36.488
2014	36.537
2015	36.029
2016	35.48
2017	35.678
2018	35.525
2019	35.396
2020	35.337
2021	35.244
2022	35.15