Year	Number
1999	23.5
2000	23.31494
2001	22.81694
2003	20.75066
2004	23.23186
2005	23.62341
2006	22.93853
2007	22.88272
2008	22.61592
2009	22.63613
2010	22.24335
2011	21.89921
2012	21.56275
2013	22.57321
2014	22.39466
2015	20.43642
2016	20.50666
2017	19.58631
2018	19.78332