Quarter	Percent
1998-01-01	37.3
1998-04-01	36.6
1998-07-01	38
1998-10-01	37.5
1999-01-01	36.9
1999-04-01	37.6
1999-07-01	37.4
1999-10-01	38.1
2000-01-01	36.3
2000-04-01	35.6
2000-07-01	36.1
2000-10-01	36.7
2001-01-01	34
2001-04-01	33.9
2001-07-01	34.4
2001-10-01	33.2
2002-01-01	33.8
2002-04-01	33.1
2002-07-01	33.7
2002-10-01	32.1
2003-01-01	32.2
2003-04-01	31.4
2003-07-01	30.8
2003-10-01	30.4
2004-01-01	34.3
2004-04-01	34.2
2004-07-01	32.7
2004-10-01	32.5
2005-01-01	31.1
2005-04-01	30.6
2005-07-01	30.6
2005-10-01	29.5
2006-01-01	30.1
2006-04-01	28.5
2006-07-01	28.3
2006-10-01	27.5
2007-01-01	27.4
2007-04-01	27.6
2007-07-01	27.7
2007-10-01	27.3
2008-01-01	25.7
2008-04-01	26.5
2008-07-01	25.5
2008-10-01	26.6
2009-01-01	27.5
2009-04-01	27.1
2009-07-01	27.9
2009-10-01	27.1
2010-01-01	27.2
2010-04-01	26.7
2010-07-01	27.2
2010-10-01	27.1
2011-01-01	26.5
2011-04-01	26.2
2011-07-01	26.2
2011-10-01	27.4
2012-01-01	27.1
2012-04-01	27.2
2012-07-01	27.1
2012-10-01	26.7
2013-01-01	25.6
2013-04-01	25.4
2013-07-01	24.8
2013-10-01	25.3
2014-01-01	25.5
2014-04-01	26.2
2014-07-01	26.5
2014-10-01	26.1
2015-01-01	24.7
2015-04-01	24.2
2015-07-01	24.4
2015-10-01	23.9
2016-01-01	21.8
2016-04-01	22.9
2016-07-01	23.4
2016-10-01	23.4
2017-01-01	24.3
2017-04-01	24.7
2017-07-01	23.2
2017-10-01	23.5
2018-01-01	21.9
2018-04-01	22.3