Year Number 1995 35.12202 1999 17.43115 2000 19.67009 2001 18.84711 2002 18.90387 2003 19.13273 2004 17.94168 2005 18.64831 2006 22.20117 2007 18.65314 2009 18.57329 2010 20.3617 2012 17.31217 2014 17.41565 2015 17.15369 2016 17.63607