Year	Percent
1991	19.6424
1992	19.7537
1993	19.31219
1994	18.69007
1995	18.13732
1996	17.10311
1997	16.85409
1998	16.19948
1999	16.68904
2000	16.48448
2001	16.42181
2002	16.52522
2003	16.67527
2004	17.1391
2005	16.62384
2006	15.61822
2007	14.6832
2008	13.8447
2009	13.43194
2010	12.6562
2011	11.98905
2012	11.46919
2013	11.16574
2014	10.33493
2015	10.20263
2016	10.13742
2017	9.45545
2018	9.25931
2019	9.05034