Year	Percent
1991	51.53
1992	54.64
1993	55.4
1994	55.96
1995	56.05
1996	54.63
1997	52.59
1998	50.32
1999	48.35
2000	46.24
2001	43.31
2002	41.42
2003	41.23
2004	38.27
2005	40.18
2006	37.27
2007	33.94
2008	30.84
2009	30.35
2010	28.32
2011	28.16
2012	28.48
2013	29.42
2014	30.92
2015	32.38
2016	34.56
2017	36.41
2018	38.11
2019	37.55