Year	Number of
1990	24.63
1991	24.26
1992	23.88
1993	24.36
1994	25.3
1995	25.3
1996	26.54
1997	26.71
1998	27.29
1999	28.42
2000	28.79
2001	29.43
2002	28.48
2003	29.07
2004	29.43
2005	28.09
2006	27.75
2007	26.21
2008	26.14
2009	25.39
2010	24.26
2011	24.19
2012	23.68
2013	23.02
2014	22.77
2015	22.61
2016	22.54