Year	Number of
1990	13.8
1991	13.67
1992	13.41
1993	13.21
1994	13.37
1995	13.11
1996	14.31
1997	14.98
1998	15.19
1999	15.2
2000	15.89
2001	16.64
2002	16.95
2003	18.16
2004	19.88
2005	21.12
2006	22.72
2007	23.27
2008	24.06
2009	25.16
2010	25.36
2011	25.63
2012	26.74
2013	28.26
2014	30.16
2015	31.56
2016	34.19