Year	Number of
1990	19.55
1991	20.04
1992	20.66
1993	21.15
1994	21.49
1995	21.8
1996	22.56
1997	23.51
1998	24.55
1999	26.31
2000	28.07
2001	29.26
2002	30.27
2003	31.03
2004	31.76
2005	32.82
2006	33.72
2007	34.65
2008	35.56
2009	36.69
2010	37.67
2011	38.88
2012	40.29
2013	41.79
2014	43.19
2015	44.11
2016	45.11