Year	Number
1991	8.349153084436123
1992	6.794237523948376
1996	5.834640584356191
1997	7.517011519568769
1998	7.935498360710743
1999	8.207801842666582
2000	7.5137831173390035
2001	9.210156604379998
2002	11.242012923167085
2003	12.435472721734776
2004	12.964614011745377
2005	12.367732511059996
2006	12.436988486901907
2007	13.728349049629912
2008	14.066790096195554
2009	19.361408269503993
2010	16.764076301365698
2011	15.120061751289413
2012	14.670228532261062
2013	15.357800629568743
2014	14.905462403496928
2015	14.896003266678463
2016	14.306278817412569
2017	13.310100254814627
2018	11.696543540776482
2019	12.299682202087292
2020	14.246254386252744
2021	11.489870167075473
2022	10.165508789434753
2023	11.200771132194019