Year	Number of
1990	23.6
1991	23.94
1992	23.74
1993	25.05
1994	25.6
1995	26.73
1996	27.65
1997	27.75
1998	28.01
1999	28.47
2000	28.99
2001	29.55
2002	30.21
2003	31.24
2004	32.9
2005	34.32
2006	35.36
2007	35.51
2008	35.36
2009	36.19
2010	37.07
2011	37.72
2012	38.96
2013	39.92
2014	41
2015	42.13
2016	43.36