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