Quarter	Percent
1998-04-01	21.5
1999-04-01	22.3
2000-04-01	22
2001-04-01	20.5
2002-04-01	19.4
2003-04-01	19.5
2004-04-01	19.2
2005-04-01	18.7
2006-04-01	18.8
2007-04-01	18.1
2008-04-01	16.4
2009-04-01	16.1
2010-01-01	18.4
2010-04-01	18.0
2010-07-01	18.0
2010-10-01	17.8
2011-01-01	17.2
2011-04-01	17.4
2011-07-01	17.6
2011-10-01	16.4
2012-01-01	16.7
2012-04-01	16.5
2012-07-01	16.3
2012-10-01	16.1
2013-01-01	16.4
2013-04-01	16.5
2013-07-01	16.6
2013-10-01	16.3
2014-01-01	15.8
2014-04-01	15.5
2014-07-01	15.4
2014-10-01	14.3
2015-01-01	15.0
2015-04-01	15.0
2015-07-01	15.6
2015-10-01	15.1
2016-01-01	13.5
2016-04-01	15.0
2016-07-01	15.2
2016-10-01	14.2
2017-01-01	14.0
2017-04-01	14.8
2017-07-01	14.7
2017-10-01	14.3
2018-01-01	13.9
2018-04-01	13.9