Year	Number
1975	4.733596809798883
1976	4.255468489233461
1977	4.557942615021433
1978	5.409446228060473
1979	6.535456997618399
1980	5.890381937898436
1981	4.59053368046869
1982	5.020704092987814
1983	4.9527413754651395
1984	4.466265459420043
1985	4.568765344295955
1986	4.538897137058505
1987	5.038209208994862
1988	4.119758503716858
1989	4.162173879536131
1990	3.838398634570317
1991	3.972290628220139
1992	3.072198986909998
1993	3.3917926048313087
1994	3.422035662775865
1995	2.7891292530921032
1996	3.0551805838999764
1997	3.040853614645402
1998	2.540825462678609
1999	2.1655700574934227
2000	1.9075478139821522
2001	1.8311975590458902
2002	2.149815207697307
2003	1.950261704408192
2004	1.6328270849528976
2005	1.4474110957550612
2006	1.440331586437092
2007	1.4307415856034371
2008	1.2296212274369955
2009	1.925958748318992
2010	2.0671682621188077
2011	1.87763757431287
2012	2.2115204940499327
2013	1.8488076288571487
2014	1.7337807035019663
2015	1.8559351960625765
2016	1.943071069106363
2017	1.9816900070328203
2018	1.8167261726893482
2019	2.0861356424202278
2020	2.8359626924456487
2021	2.4661413282556386
2022	2.097959962718866
2023	2.0320688137522014