Year	Number
1997	3.9110726017213593
1998	3.6478198902035603
1999	3.3344878049341053
2000	3.387797013871781
2001	4.267025524218246
2002	4.639947611215148
2003	6.006016038628248
2004	4.068051199406999
2005	5.566784770655202
2006	5.119290486719568
2007	5.49931646967076
2008	6.362327808734085
2009	7.641654074777689
2010	4.707882835723573
2011	4.187493134774048
2012	4.211056990257864
2013	4.247733852826583
2014	3.243610503460137
2015	4.598982384293801
2016	4.028443534633596
2017	3.5865317513831987
2018	2.6226852910360394
2019	2.9260756652805795
2020	5.52294491311846
2021	4.387171462251222
2022	3.4703365827579256