Year	Number of
1990	30.89
1991	32.11
1992	33.37
1993	34.73
1994	36.17
1995	37.77
1996	39.34
1997	40.72
1998	43.9
1999	48.17
2000	52.41
2001	55.99
2002	58.81
2003	63.3
2004	67.41
2005	72.12
2006	76.25
2007	81.24
2008	86.13
2009	93.62
2010	102.92
2011	113.8
2012	122.28
2013	132.89
2014	141.21
2015	149.33
2016	157.06