Year	Percent
1990	67.16
1991	67.58
1992	68.03
1993	68.44
1994	68.77
1995	69.18
1996	69.55
1997	69.92
1998	70.27
1999	70.58
2000	70.85
2001	71.25
2002	71.69
2003	72.12
2004	72.49
2005	72.79
2006	73.08
2007	73.23
2008	73.26
2009	73.21
2010	73.14
2011	73.29
2012	73.47
2013	73.63
2014	73.73
2015	73.78
2016	73.86
2017	73.98
2018	74.15
2019	74.28