Year	Number of
1990	17.09
1991	17.34
1992	17.69
1993	18.11
1994	18.58
1995	19.1
1996	19.64
1997	20.23
1998	20.89
1999	21.65
2000	22.54
2001	23.41
2002	24.4
2003	25.52
2004	26.75
2005	28.11
2006	29.42
2007	30.8
2008	32.32
2009	33.98
2010	35.82
2011	37.23
2012	38.79
2013	40.46
2014	42.25
2015	44.17
2016	46.1