Year	Percent
1990	40.99
1991	40.82
1992	40.65
1993	40.47
1994	40.3
1995	40.13
1996	40
1997	39.48
1998	38.94
1999	38.38
2000	37.8
2001	37.26
2002	36.71
2003	36.13
2004	35.53
2005	34.91
2006	34.33
2007	33.72
2008	33.1
2009	32.48
2010	31.85
2011	31.24
2012	30.84
2013	30.64
2014	30.48
2015	30.23
2016	30.01
2017	29.78
2018	29.74
2019	29.7