Year	Number of
1990	22.6
1991	22.41
1992	22.26
1993	22.2
1994	22.23
1995	22.31
1996	22.34
1997	22.42
1998	22.52
1999	23.1
2000	23.64
2001	24.12
2002	24.74
2003	25.54
2004	26.3
2005	26.72
2006	27.5
2007	27.8
2008	30.71
2009	34.42
2010	35.4
2011	36.28
2012	37.54
2013	39.43
2014	41.34
2015	43.03
2016	44.57