Year	Percent
1990	67.709
1991	68.219
1992	68.726
1993	69.227
1994	69.724
1995	70.216
1996	70.705
1997	71.187
1998	71.524
1999	71.747
2000	71.969
2001	72.189
2002	72.409
2003	72.627
2004	72.845
2005	73.061
2006	73.276
2007	73.491
2008	73.704
2009	73.923
2010	74.149
2011	74.381
2012	74.619
2013	74.863
2014	75.113
2015	75.368
2016	75.628
2017	75.894