Quarter	Percent
1998-01-01	41.9
1998-04-01	41
1998-07-01	40.6
1998-10-01	40.5
1999-01-01	41
1999-04-01	40.4
1999-07-01	40.1
1999-10-01	40.2
2000-01-01	40.6
2000-04-01	40.1
2000-07-01	39.5
2000-10-01	39.3
2001-01-01	39.7
2001-04-01	39.7
2001-07-01	39.1
2001-10-01	39.1
2002-01-01	39.3
2002-04-01	39
2002-07-01	38.7
2002-10-01	38.7
2003-01-01	38.9
2003-04-01	38.4
2003-07-01	38.3
2003-10-01	38.4
2004-01-01	37.5
2004-04-01	37.2
2004-07-01	37.3
2004-10-01	36.8
2005-01-01	37.5
2005-04-01	37.4
2005-07-01	38.1
2005-10-01	37.1
2006-01-01	37.3
2006-04-01	37.1
2006-07-01	37.8
2006-10-01	37.2
2007-01-01	38.2
2007-04-01	37.6
2007-07-01	37.5
2007-10-01	37.1
2008-01-01	37.3
2008-04-01	36.6
2008-07-01	37.3
2008-10-01	37.2
2009-01-01	37.7
2009-04-01	37.5
2009-07-01	38.1
2009-10-01	37.6
2010-01-01	37.8
2010-04-01	37.7
2010-07-01	38.7
2010-10-01	37.7
2011-01-01	38
2011-04-01	38.1
2011-07-01	38.5
2011-10-01	37.2
2012-01-01	36.7
2012-04-01	36.2
2012-07-01	37.1
2012-10-01	36.1
2013-01-01	36.4
2013-04-01	36.7
2013-07-01	37.3
2013-10-01	36.2
2014-01-01	36.1
2014-04-01	36.4
2014-07-01	36.4
2014-10-01	35.3
2015-01-01	36.1
2015-04-01	35.8
2015-07-01	36.4
2015-10-01	35.5
2016-01-01	35.8
2016-04-01	34.7
2016-07-01	35.2
2016-10-01	34.5
2017-01-01	34.7
2017-04-01	34.6
2017-07-01	34.6
2017-10-01	34.3
2018-01-01	34.6
2018-04-01	33.7