Year	Number
1977	3.4763727908250655
1978	3.1069532442264345
1979	6.009742129704089
1980	4.737364626900937
1981	3.4777824895352096
1982	3.580124563791963
1983	3.149066996927075
1984	2.864399472885935
1985	3.376519424249759
1986	3.332550928615804
1987	3.5147562153782324
1988	3.6338414480220447
1989	4.257823409171504
1990	2.6863646732315445
1991	3.2873802628979747
1992	3.561046934945265
1993	4.383390032794499
1994	4.760293293160789
1995	3.6737365572994234
1996	3.521798213492421
1997	3.2373155779911356
1998	3.3303820901216468
1999	3.418107478609582
2000	3.3915676018069307
2001	3.7299441272245657
2002	4.218453255626242
2003	4.395230116488012
2004	4.198018567870221
2005	9.155299458667352
2006	8.124979072472374
2007	7.116214415601166
2008	6.092328138741674
2009	7.389670058412438
2010	6.7923454036702635
2011	4.644324871704383
2012	4.629675787349472
2013	4.845381436530831
2014	4.815875463734971
2015	5.546363373866632
2016	6.012775125372635
2017	6.005956339458513
2018	5.300465249007947
2019	5.836410051992795
2020	8.419873237380859
2021	5.79504405159356
2022	4.744450231120605
2023	5.351564856101867