Year	Percent
1997	15.8935
1998	16.6772
1999	18.7708
2000	19.343
2001	18.0519
2002	22.4303
2003	19.1699
2004	25.1368
2005	21.5536
2006	22.3262
2007	21.0816
2008	18.817
2009	21.231
2010	22.1038
2011	24.0412
2012	22.224
2013	23.1633
2014	23.5859
2015	20.5682
2016	19.8602
2017	18.1087