Year	Number of
1990	38.33
1991	36.78
1992	37
1993	36.98
1994	37.14
1995	38.35
1996	37.26
1997	35.56
1998	34.31
1999	32.9
2000	32.96
2001	32.22
2002	30.47
2003	30.18
2004	29.89
2005	29.6
2006	29.04
2007	28.69
2008	29.15
2009	29.12
2010	28.48
2011	28.51
2012	28.57
2013	28.78
2014	28.81
2015	28.8
2016	28.96