Year	Number
1999	18.79335
2000	18.47298
2001	20.03743
2002	20.05477
2003	18.66596
2004	21.62135
2005	21.27628
2006	15.48962
2007	19.79364
2008	19.65812
2009	20.83217
2011	25.19684
2012	21.7278
2013	22.24559
2014	18.7034
2015	19.50429
2016	22.13073
2017	21.69872
2018	23.37084
2019	19.60274