Year	Number of
1990	16.94
1991	17.6
1992	18.18
1993	18.69
1994	19.54
1995	20.49
1996	20.17
1997	20.33
1998	19.74
1999	20.04
2000	20.45
2001	20.3
2002	21.11
2003	22.15
2004	23.02
2005	23.65
2006	24.5
2007	25.75
2008	26.2
2009	26.73
2010	27.48
2011	28.12
2012	28.14
2013	28.66
2014	29
2015	29.38
2016	28.39