Year	Number of
1990	17.45
1991	17.73
1992	18.06
1993	18.52
1994	19
1995	19.36
1996	20.19
1997	20.77
1998	21.43
1999	22.22
2000	23.05
2001	23.48
2002	23.91
2003	24.53
2004	24.78
2005	25.49
2006	26.55
2007	27.18
2008	27.93
2009	29.18
2010	29.86
2011	30.3
2012	31.15
2013	32.11
2014	34.01
2015	35.51
2016	37.69