Year	Percent
1998-01-01	21.7
1999-01-01	21.2
2000-01-01	19.4
2001-01-01	17.5
2002-01-01	16.6
2003-01-01	15.9
2004-01-01	17.8
2005-01-01	17.6
2006-01-01	21.4
2007-01-01	20.8
2008-01-01	18.4
2009-01-01	19.6
2010-01-01	20.3
2011-01-01	19.3
2012-01-01	19
2013-01-01	18.4
2014-01-01	18.4
2015-01-01	19.1