Year	Number
1976	3.325044266654849
1977	3.1066560711901436
1978	3.528676966238644
1979	3.4876736977044054
1980	3.55327970335433
1981	2.5940340140360507
1982	3.4549027420404874
1983	3.307128529876695
1984	2.832102568031455
1985	3.0196035483766615
1986	3.2045088125349164
1987	3.663471093403735
1988	2.9558648567677452
1989	3.131932415008693
1990	4.002338584199838
1991	3.0800662340305265
1992	3.379431794554163
1993	3.7488764921712447
1994	3.7428635064872524
1995	3.447552072623718
1996	4.272990681822463
1997	4.7054285317163975
1998	5.337778994397015
1999	5.6508293521268556
2000	4.677522838625061
2001	4.093612996472215
2002	3.83808988346727
2003	4.197727070252527
2004	3.763483453063254
2005	3.0977883106527555
2006	2.869424115260913
2007	2.872774485298318
2008	3.090503166140636
2009	4.654101043346713
2010	3.7630315447491305
2011	2.749254365377146
2012	3.3301862271877654
2013	2.6954349742861377
2014	2.6520472382345583
2015	2.7541237717949376
2016	3.2124678285623283
2017	3.3216434293632098
2018	3.0550969474858336
2019	3.7962533741021742
2020	3.0838176746130115
2021	2.3681627252636037