Year	Number of
1990	15.77
1991	16.26
1992	16.75
1993	17.27
1994	17.83
1995	18.44
1996	19.6
1997	20.88
1998	22.26
1999	23.72
2000	25.26
2001	26.31
2002	27.34
2003	28.38
2004	29.45
2005	30.59
2006	31.21
2007	31.89
2008	32.66
2009	33.52
2010	34.48
2011	35.3
2012	36.21
2013	37.15
2014	38.18
2015	39.27
2016	40.4