Year	Number
1960	1.725691168897969
1961	1.616469807979368
1962	1.5845852276032726
1963	1.472073204239825
1964	1.449265388444239
1965	1.4964398895047137
1966	1.4651122844321711
1967	1.5295279516515927
1968	1.7250067846856312
1969	2.041340265425631
1970	2.492418955953883
1971	2.972261165723621
1972	2.924594033056009
1973	2.7654945687845074
1974	2.2405731258557213
1975	2.8366382343581895
1976	3.2430760328445696
1977	3.707413966080418
1978	3.825149609635647
1979	3.59580142720374
1980	4.491402966355577
1981	5.427252273123563
1982	6.460592926101092
1983	8.365641260850985
1984	9.264009128689457
1985	8.042234734698937
1986	7.50462703155806
1987	6.647874438377903
1988	5.837099399968682
1989	4.905801138400487
1990	4.558838372565095
1991	4.230894290119154
1992	4.262967583493327
1993	4.237293723955746
1994	3.966857591020931
1995	3.864837130494405
1996	4.017629717558456
1997	5.5759325828829525
1998	4.2382830163752185
1999	4.086349360932769
2000	4.3030094209592935
2001	4.469511246728436
2002	3.97726666395397
2003	4.037768567896815
2004	3.726488608828791
2005	3.784645799288974
2006	3.3774880707329364
2007	3.016989083094127
2008	2.6890499606239056
2009	2.2371343421932797
2010	2.1609229701131243
2011	2.5427663049306153
2012	2.6532155845742516
2013	3.1260241154683346
2014	3.292907891701881
2015	3.276097733516488
2016	3.0176400121684606
2017	2.7949609362404604
2018	3.0266028837569623
2019	2.9919470961192776
2020	2.8424338089454175
2021	3.0584836636636283
2022	3.2926901868138385
2023	3.261839521256599