Year	Percent
1997	23.13808
1998	22.6278
1999	22.50251
2000	22.40444
2001	21.45513
2002	20.58736
2003	20.69918
2004	20.95524
2005	21.22266
2006	21.59697
2007	21.45314
2008	20.96761
2009	19.629
2010	19.7846
2011	20.00458
2012	19.91158
2013	20.06563
2014	20.22827
2015	19.44186
2016	18.88043