Year	Percent
1990	29
1991	29.05
1992	29.11
1993	29.17
1994	29.23
1995	29.29
1996	29.34
1997	29.4
1998	29.46
1999	29.52
2000	29.58
2001	29.67
2002	29.76
2003	29.86
2004	29.94
2005	30.03
2006	30.12
2007	30.2
2008	30.29
2009	30.37
2010	30.46
2011	30.53
2012	30.6
2013	30.67
2014	30.74
2015	30.81