Year	Number of
1990	16.61
1991	16.95
1992	17.31
1993	17.67
1994	18.07
1995	18.52
1996	18.95
1997	19.44
1998	19.95
1999	20.49
2000	21.07
2001	21.39
2002	21.74
2003	22.09
2004	22.5
2005	22.98
2006	23.55
2007	24.18
2008	24.87
2009	25.64
2010	26.49
2011	27.11
2012	27.79
2013	28.5
2014	29.29
2015	30.15
2016	31.11