Year	Percent
1991	34.87
1992	34.9
1993	34.94
1994	35.07
1995	35.26
1996	35.34
1997	35.48
1998	35.67
1999	35.87
2000	36.15
2001	36.4
2002	36.66
2003	36.99
2004	37.4
2005	37.85
2006	38.26
2007	38.66
2008	39
2009	39.07
2010	39.32
2011	39.57
2012	39.77
2013	39.92
2014	40.09
2015	40.17
2016	40.31
2017	40.45
2018	40.55
2019	40.58
2020	38.81