Year	Number of
1990	11.45
1991	12.09
1992	12.75
1993	13.44
1994	14.03
1995	14.41
1996	14.62
1997	14.85
1998	14.94
1999	14.81
2000	14.87
2001	15.18
2002	15.92
2003	16.88
2004	17.3
2005	17.45
2006	18.09
2007	18.97
2008	20.26
2009	21.52
2010	23.01
2011	23.67
2012	24.41
2013	25.05
2014	25.92
2015	26.92
2016	27.64