Year	Number of
1990	115.59
1991	116.09
1992	111.85
1993	104.49
1994	97.11
1995	91.79
1996	97.62
1997	107.87
1998	122.47
1999	139.71
2000	158.67
2001	168.71
2002	178.79
2003	189.75
2004	203.25
2005	220.71
2006	239.52
2007	263.2
2008	292.03
2009	325.47
2010	363.62
2011	399.09
2012	438.64
2013	481.75
2014	526.5
2015	571.95
2016	612.89