Year	Percent
1990	28.77
1991	29.49
1992	30.22
1993	30.94
1994	31.67
1995	32.4
1996	33.12
1997	33.85
1998	34.58
1999	35.3
2000	37.7
2001	38.56
2002	39.5
2003	40.43
2004	41.3
2005	42.17
2006	42.85
2007	43.53
2008	44.21
2009	44.89
2010	45.56
2011	45.98
2012	46.4
2013	46.81
2014	47.23
2015	47.64