Year	Percent
1991	31.61
1992	29.95
1993	25
1994	23.87
1995	24.17
1996	23.63
1997	24.88
1998	26.65
1999	29.99
2000	32.41
2001	33.71
2002	34.18
2003	34.37
2004	34.67
2005	38.33
2006	39.46
2007	39.18
2008	36.01
2009	28
2010	24.9
2011	21.83
2012	18.15
2013	16.58
2014	16.56
2015	17.94
2016	18.5
2017	20.78
2018	22.06
2019	22.61