Year	Number of
1990	24.86
1991	24.94
1992	25.01
1993	25.13
1994	25.31
1995	25.5
1996	25.55
1997	25.57
1998	25.54
1999	25.24
2000	25.02
2001	24.57
2002	24.34
2003	24.27
2004	24.12
2005	23.7
2006	23.53
2007	22.73
2008	22.12
2009	22.61
2010	24.1
2011	23.93
2012	24.21
2013	25.06
2014	26.02
2015	27.04
2016	28.04