Year Number of 1990 415.95 1991 452.24 1992 443.09 1993 440.11 1994 440.94 1995 451.92 1996 465.87 1997 472.85 1998 477.86 1999 490.73 2000 492.44 2001 497.56 2002 501.5 2003 515.81 2004 514.35 2005 516.11 2006 522.27 2007 531 2008 529.73 2009 530.35 2010 548.76 2011 552.98 2012 560.76 2013 558.73 2014 557.51 2015 565.48 2016 574.15