Year	Number of
1990	57.45
1991	59.48
1992	61.61
1993	63.87
1994	66.26
1995	68.85
1996	71.29
1997	73.89
1998	76.65
1999	79.6
2000	82.79
2001	85.61
2002	88.61
2003	91.87
2004	95.31
2005	98.98
2006	102.25
2007	105.66
2008	109.46
2009	113.53
2010	117.97
2011	122.11
2012	126.59
2013	131.15
2014	136.14
2015	141.62
2016	147.84