Year	Number of
1990	14.54
1991	15.58
1992	16.5
1993	16.99
1994	17.09
1995	16.83
1996	16.82
1997	17.02
1998	17.27
1999	17.53
2000	17.66
2001	17.89
2002	18.24
2003	19.43
2004	21.2
2005	22.47
2006	23.22
2007	24.07
2008	24.73
2009	25.33
2010	25.74
2011	26.44
2012	27.17
2013	27.8
2014	28.49
2015	29.18
2016	29.7