Year	Number
1999	19.87342
2000	19.32176
2001	18.18973
2002	18.24504
2003	17.36361
2004	17.87927
2005	18.05363
2006	18.11352
2007	16.91239
2008	16.63814
2009	17.36945
2011	16.179
2012	16.13763
2013	15.48667
2014	14.6047
2015	15.3958
2016	15.00838
2017	13.44513
2018	13.38026
2019	13.10283