Year	Percent
1998	31.42
1999	30.63
2000	29.48
2001	31.45
2002	28.28
2003	28.79
2004	27.86
2005	28.49
2006	28.72
2007	28.38
2008	25.69
2009	24.14
2010	22.56
2011	23.38
2012	22.75
2013	21.79
2014	21.39
2015	20.52
2016	20.75
2017	19.96