Year	Number of
1990	15.47
1991	14.97
1992	14.59
1993	14.43
1994	14.89
1995	16.19
1996	16.84
1997	17.44
1998	18.42
1999	17.52
2000	17.67
2001	17.82
2002	18.56
2003	18.66
2004	18.32
2005	18.64
2006	18.32
2007	18.63
2008	19.03
2009	19.61
2010	20.2
2011	21.16
2012	22.02
2013	23.47
2014	24.66
2015	25.81
2016	27.39