Year	Percent
1990	22.87
1991	23.66
1992	24.45
1993	25.24
1994	26.03
1995	26.82
1996	27.61
1997	28.39
1998	29.18
1999	29.97
2000	30.76
2001	31.45
2002	32.13
2003	32.82
2004	33.51
2005	34.2
2006	34.88
2007	35.56
2008	36.25
2009	36.93
2010	37.61
2011	38.3
2012	38.99
2013	39.67
2014	40.36
2015	41.05