Year	Number of
1990	12.32
1991	12.63
1992	12.89
1993	13.12
1994	13.28
1995	13.48
1996	13.91
1997	14.07
1998	14.22
1999	14.36
2000	14.73
2001	14.85
2002	15.17
2003	15.5
2004	15.93
2005	16
2006	15.92
2007	16.08
2008	16.46
2009	16.63
2010	16.5
2011	16.52
2012	16.77
2013	17
2014	17.46
2015	17.97
2016	18.53