Year	Number of
1990	18.68
1991	17.56
1992	16.85
1993	17.5
1994	17.04
1995	16.72
1996	17.28
1997	17.29
1998	17.54
1999	17.88
2000	18.11
2001	18.02
2002	18.1
2003	18.62
2004	19.81
2005	21.28
2006	21.65
2007	22.07
2008	22.76
2009	22.84
2010	23.05
2011	23.54
2012	24.58
2013	25.59
2014	26.84
2015	28.69
2016	31.05