Year	Number of
1990	15.48
1991	16
1992	15.73
1993	15.2
1994	16.02
1995	17.24
1996	19.57
1997	19.57
1998	21.25
1999	21.63
2000	23
2001	24.17
2002	24.54
2003	25.01
2004	24.95
2005	24.87
2006	25.01
2007	25.22
2008	25.6
2009	25.92
2010	26.05
2011	25.92
2012	25.8
2013	25.71
2014	25.49
2015	24.87
2016	24.85