Year	Number of
1990	14.2
1991	14.3
1992	14.31
1993	14.29
1994	14.34
1995	14.44
1996	14.82
1997	15.28
1998	15.88
1999	16.43
2000	17
2001	17.76
2002	18.59
2003	19.47
2004	20.35
2005	21.23
2006	22.07
2007	22.89
2008	23.68
2009	24.5
2010	25.39
2011	26.25
2012	27.19
2013	28.21
2014	29.28
2015	30.42
2016	31.69