Year	Percent
1991	39.39
1992	39.18
1993	38.87
1994	38.57
1995	38.28
1996	38.01
1997	37.79
1998	37.52
1999	37.13
2000	36.75
2001	35.44
2002	34.08
2003	32.77
2004	31.51
2005	30.29
2006	29.13
2007	28.01
2008	26.9
2009	25.63
2010	24.47
2011	23.36
2012	22.27
2013	21.32
2014	20.42
2015	19.54
2016	18.69
2017	17.87
2018	17.74
2019	17.59