Year Number of 1990 167.69 1991 179.03 1992 192.99 1993 205.35 1994 214.96 1995 224.2 1996 235.92 1997 245.71 1998 260.79 1999 266.03 2000 280.35 2001 290.11 2002 311.69 2003 326.42 2004 337.6 2005 348.34 2006 361.61 2007 375.11 2008 389.28 2009 403.62 2010 418.96 2011 440.02 2012 461.03 2013 477.23 2014 498.21 2015 520.57 2016 551.04