Year	Number of
1990	12.28
1991	12.87
1992	13.3
1993	13.68
1994	14.07
1995	14.51
1996	14.68
1997	14.63
1998	14.43
1999	14.17
2000	14.33
2001	14.85
2002	15.38
2003	16.17
2004	17.2
2005	18.69
2006	20.12
2007	21.68
2008	22.94
2009	24.17
2010	25.23
2011	27.15
2012	29.04
2013	30.85
2014	33.19
2015	36.03
2016	38.49