Year	Number of
1990	18.29
1991	18.47
1992	18.75
1993	19.33
1994	20.12
1995	20.83
1996	21.75
1997	22.37
1998	22.76
1999	23.03
2000	23.55
2001	24.05
2002	24.26
2003	24.53
2004	24.75
2005	25.35
2006	26.06
2007	26.3
2008	26.57
2009	27.28
2010	27.57
2011	28.02
2012	28.94
2013	30.03
2014	31.5
2015	32.7
2016	34.09