Year	Percent
1998-01-01	22.5
1999-01-01	23.7
2000-01-01	22.2
2001-01-01	22
2002-01-01	19.7
2003-01-01	18.4
2004-01-01	17.3
2005-01-01	21.1
2006-01-01	20.2
2007-01-01	19.3
2008-01-01	15.6
2009-01-01	16.7
2010-01-01	18.9
2011-01-01	18.5
2012-01-01	18
2013-01-01	18.9
2014-01-01	16.9
2015-01-01	16.9