Quarter	Percent
1998-04-01	32.8
1999-04-01	30.6
2000-04-01	31.6
2001-01-01	30.5
2001-04-01	30.7
2001-07-01	29.7
2001-10-01	29.2
2002-01-01	29
2002-04-01	28.7
2002-07-01	28.7
2002-10-01	28.6
2003-01-01	28.6
2003-04-01	28.2
2003-07-01	27.8
2003-10-01	27.7
2004-01-01	27.6
2004-04-01	27.4
2004-07-01	27
2004-10-01	27.2
2005-01-01	27
2005-04-01	28.1
2005-07-01	27.3
2005-10-01	26.7
2006-01-01	26.4
2006-04-01	27.2
2006-07-01	27.6
2006-10-01	27.4
2007-01-01	27.4
2007-04-01	27.1
2007-07-01	26.9
2007-10-01	27.2
2008-01-01	27.6
2008-04-01	27.5
2008-07-01	27
2008-10-01	26.8
2009-01-01	26.3
2009-04-01	26.6
2009-07-01	26.1
2009-10-01	25.5
2010-01-01	25.6
2010-04-01	25.6
2010-07-01	25.1
2010-10-01	24.7
2011-01-01	24.4
2011-04-01	23.9
2011-07-01	24.1
2011-10-01	23.7
2012-01-01	23.7
2012-04-01	23
2012-07-01	23.1
2012-10-01	22.3
2013-01-01	22.8
2013-04-01	22.7
2013-07-01	22.4
2013-10-01	22
2014-01-01	22.1
2014-04-01	21.6
2014-07-01	21.8
2014-10-01	21.7
2015-01-01	21.5
2015-04-01	21.4
2015-07-01	21.6
2015-10-01	20.9
2016-01-01	20.9
2016-04-01	20.5
2016-07-01	19.8
2016-10-01	20.0
2017-01-01	19.7
2017-04-01	19.1
2017-07-01	19.4
2017-10-01	19.8
2018-01-01	19.1
2018-04-01	18.6