Year	Number of
1990	31.34
1991	31.68
1992	31.99
1993	32.49
1994	33
1995	33.63
1996	34.11
1997	34.69
1998	35.08
1999	35.65
2000	36.14
2001	36.42
2002	36.67
2003	36.91
2004	37.19
2005	37.4
2006	37.63
2007	37.78
2008	38.01
2009	38.4
2010	38.81
2011	38.82
2012	41.33
2013	41.91
2014	42.76
2015	43.73
2016	44.78