Year	Number of
1990	19.56
1991	20.14
1992	20.75
1993	21.4
1994	22.07
1995	22.82
1996	23.33
1997	23.87
1998	24.42
1999	24.94
2000	25.45
2001	25.24
2002	24.96
2003	24.64
2004	24.33
2005	24.11
2006	24.12
2007	24.17
2008	24.3
2009	24.46
2010	24.65
2011	25.03
2012	25.44
2013	25.87
2014	26.3
2015	26.71
2016	27.2