Year	Number of
1990	60.72
1991	60.36
1992	60.89
1993	61.55
1994	62.31
1995	63.68
1996	65.69
1997	67.09
1998	70.74
1999	73.4
2000	75.82
2001	76.21
2002	77.66
2003	81.39
2004	86.19
2005	91.52
2006	97.84
2007	103.46
2008	108.35
2009	113.47
2010	117.92
2011	122.35
2012	129.8
2013	137.28
2014	145.34
2015	153.18
2016	160.27