Year	Number
1991	5.4115935437718585
1992	4.830212189098627
1993	4.53362854240436
1994	4.425868949754502
1995	4.349849814171905
1996	4.249446672396111
1997	3.1737918953314463
1998	3.651286701162589
1999	3.676280848931746
2000	3.581237799953004
2001	3.4518915838412867
2002	3.4476732602072477
2003	3.4692650018838553
2004	3.596612334019796
2005	3.7648006950967012
2006	4.0225447935281515
2007	4.026734726237244
2008	3.47210218144792
2009	2.6412918721534333
2010	2.6821756618879236
2011	2.8202557229654515
2012	2.78315487470287
2013	3.1359780344848613
2014	3.224358201991617
2015	3.153025785743556
2016	3.1156822386892933
2017	3.134014704034774
2018	3.2894616472231886
2019	3.318077363599652
2020	3.189532492856296
2021	3.250992115483176
2022	3.904714424437457
2023	4.0423002641027805