Year	Number
1960	8.576706393817348
1961	9.187950063072137
1962	9.79747759767101
1963	8.993165270324072
1964	8.861860420906945
1965	8.097295504707393
1966	7.91830075811039
1967	6.777201142509973
1968	7.278847853331535
1969	8.00081780643646
1970	8.042239903827134
1971	6.468300210319175
1972	6.690757564435385
1973	7.136365763755505
1974	6.551350184189438
1975	7.098964908915652
1976	7.402476196730191
1977	8.6999471008576
1978	7.475108385733179
1979	5.692680044290891
1980	4.6130397248772255
1981	4.5167114547103475
1982	4.0446755872948135
1983	4.151444487263285
1984	3.2181548202190307
1985	2.3894731217932637
1986	3.1439391315038905
1987	3.5968907141009425
1988	4.211971023850994
1989	4.164650201158278
1990	4.37907380550055
1991	5.033850656395579
1992	6.3054197145032065
1993	3.369548374812358
1994	3.6677404248162744
1995	3.5951480006439187
1996	3.2180723740748842
1997	3.3790990480313745
1998	4.479583244605645
1999	3.5382796342258547
2000	2.946728773241145
2001	3.973953960510197
2002	3.5022618849818534
2003	3.4663087576436737
2004	3.3111641510521097
2005	3.610819314512315
2006	3.2015238101832812
2007	3.8650520469373753
2008	4.944776328681175
2009	4.66630635111051
2010	4.745756239330021
2011	5.867576348487255
2012	5.62683757303364
2013	5.291956102237353
2014	4.708695821382143
2015	3.9288936847104012
2016	3.9882187770809367
2017	3.9393601749803704
2018	4.399874611258433
2019	3.9876927304910916
2020	3.7183165506531233
2021	4.022178092424952
2022	4.434721630769599
2023	3.631434270104284