Year Number of 1990 438.88 1991 446.1 1992 453.2 1993 465.97 1994 466.22 1995 470.67 1996 475.82 1997 482.76 1998 491.39 1999 500.75 2000 508.47 2001 521.41 2002 528.02 2003 543.54 2004 558.94 2005 576.39 2006 585.94 2007 595.39 2008 605.29 2009 617.49 2010 632.28 2011 644.3 2012 658.64 2013 672.49 2014 688.03 2015 703.98 2016 721.2