Year	Number of
1990	13.71
1991	14.72
1992	15.65
1993	16.06
1994	16.1
1995	15.85
1996	15.8
1997	15.85
1998	15.95
1999	15.93
2000	15.92
2001	15.98
2002	16.14
2003	17.14
2004	18.68
2005	19.69
2006	20.27
2007	20.99
2008	21.45
2009	21.88
2010	22.18
2011	22.73
2012	23.29
2013	23.72
2014	24.25
2015	24.75
2016	24.98