Year	Number
2004-01-01	21
2005-01-01	21
2006-01-01	19
2007-01-01	20
2008-01-01	19
2009-01-01	18
2010-01-01	16
2011-01-01	16
2012-01-01	16
2013-01-01	15
2014-01-01	17
2015-01-01	18
2016-01-01	16
2017-01-01	14