Year	Number of
1990	16.59
1991	18.81
1992	19.26
1993	20.1
1994	19.76
1995	19.45
1996	20.14
1997	20.55
1998	22.66
1999	22.64
2000	22.52
2001	22.21
2002	22.59
2003	22.62
2004	21.64
2005	22.76
2006	22.49
2007	21.84
2008	20.92
2009	22.33
2010	21.18
2011	19.72
2012	21.47
2013	22.34
2014	22.4
2015	22.74
2016	22.94