Year Number 2008-01-01 2.38661029298242 2009-01-01 2.80112152229221 2010-01-01 5.69486455363078 2011-01-01 6.52652339674480 2012-01-01 7.63382327466641 2013-01-01 7.71854573610291 2014-01-01 6.26811472957781 2015-01-01 6.55303145542304