Year	Percent
1990	31.27
1991	31.32
1992	31.38
1993	31.45
1994	31.55
1995	31.62
1996	31.42
1997	31.22
1998	31
1999	30.78
2000	30.55
2001	30.34
2002	30.13
2003	29.9
2004	29.67
2005	29.44
2006	29.21
2007	28.97
2008	28.74
2009	28.5
2010	28.26
2011	28.3
2012	28.34
2013	28.37
2014	28.4
2015	28.44
2016	28.52
2017	28.6
2018	28.67
2019	28.73