Year	Percent
1991	54.80307
1992	54.15061
1993	53.65963
1994	52.96586
1995	52.14341
1996	50.73119
1997	49.21182
1998	48.11293
1999	46.90979
2000	45.63663
2001	44.06079
2002	42.76389
2003	41.57252
2004	40.35638
2005	39.40316
2006	38.71324
2007	37.87697
2008	37.19632
2009	37.09025
2010	37.17678
2011	37.10005
2012	37.19612
2013	37.51535
2014	37.79833
2015	38.3543
2016	38.85842
2017	39.19142
2018	39.14762
2019	39.51333