Year	Percent
1990	32.36
1991	34.2
1992	36.03
1993	37.87
1994	39.71
1995	41.55
1996	43.39
1997	45.23
1998	47.07
1999	48.9
2000	50.74
2001	51.03
2002	51.32
2003	51.61
2004	51.9
2005	52.18
2006	52.56
2007	52.93
2008	53.3
2009	53.68
2010	54.05
2011	54.42
2012	54.79
2013	55.17
2014	55.54
2015	55.91