Year	Number of
1990	13.16
1991	14.54
1992	15.28
1993	15.57
1994	15.59
1995	16.42
1996	17.72
1997	18.93
1998	19.34
1999	19.52
2000	19.05
2001	19.57
2002	21.28
2003	21.75
2004	23.31
2005	23.65
2006	24.24
2007	25.5
2008	26
2009	26.45
2010	27.47
2011	27.96
2012	28.11
2013	28.75
2014	28.34
2015	29.93
2016	31.4