Year	Number of
1990	13.56
1991	13.88
1992	14.29
1993	14.75
1994	15.28
1995	15.86
1996	16.39
1997	16.97
1998	17.56
1999	18.17
2000	18.78
2001	19.45
2002	20.13
2003	20.88
2004	21.59
2005	22.28
2006	23.11
2007	23.93
2008	24.9
2009	25.97
2010	27.21
2011	28.21
2012	29.39
2013	30.69
2014	32.1
2015	33.61
2016	35.25