Year	Percent
1990	69.62
1991	69.65
1992	69.68
1993	69.72
1994	69.75
1995	69.78
1996	69.79
1997	69.76
1998	69.73
1999	69.7
2000	69.67
2001	69.66
2002	69.64
2003	69.61
2004	69.57
2005	69.5
2006	70.61
2007	71.71
2008	72.81
2009	73.92
2010	75.02
2011	76.13
2012	75.37
2013	74.59
2014	73.77
2015	72.79
2016	71.82
2017	71.83
2018	71.84
2019	71.86