Year	Percent
1990	43.01
1991	42.76
1992	42.42
1993	42.01
1994	41.56
1995	41.06
1996	40.74
1997	40.37
1998	39.97
1999	39.56
2000	39.15
2001	38.91
2002	38.67
2003	38.42
2004	38.17
2005	37.92
2006	37.82
2007	37.18
2008	36.54
2009	35.9
2010	35.29
2011	34.65
2012	34.02
2013	33.41
2014	32.82
2015	32.24
2016	31.66
2017	28.13
2018	27.82
2019	27.58