Year	Number
1960	3.288297949703338
1961	4.635392176666672
1962	4.646918655027661
1963	3.373604117985042
1964	3.163474757391777
1965	3.1039604155012155
1966	3.358554840154526
1967	3.5638471601453334
1968	3.1138856521696705
1969	3.518512489603054
1970	3.7289988446452758
1971	3.891972017049711
1972	3.3844572210475716
1973	3.9981520064011606
1974	2.6555215380394084
1975	3.090022039821288
1976	2.8232160329805427
1977	2.727161176221557
1978	2.3511554623002846
1979	2.429081435003163
1980	2.686083749224028
1981	4.093663606160464
1982	3.517030687884249
1983	3.9574796537274106
1984	5.001127885373375
1985	6.019232998081524
1986	3.5344765380379184
1987	3.195781828673594
1988	4.184661008375291
1989	3.698522969185676
1990	2.3263554524003633
1991	3.633804371428454
1992	3.28842113637218
1993	3.5287427421679487
1994	4.300210414651661
1995	4.247638534892032
1996	4.092002593205862
1997	3.4778783354393434
1998	3.1308642056141522
1999	3.0444307863570286
2000	3.180909783617993
2001	4.438478989434625
2002	4.5841547160881735
2003	3.844435168955241
2004	4.087041991051822
2005	4.437532205490601
2006	4.606618538320795
2007	4.627216318685545
2008	3.9830776660699563
2009	3.44900542488817
2010	3.7405773837978233
2011	4.234358965912125
2012	3.366469736619327
2013	3.9892919349495233
2014	4.078456801559061
2015	4.214882441030186
2016	3.7374359405707405
2017	3.7701295457586492
2018	3.997198083711308
2019	3.5714254835795223
2020	5.607359245795473
2021	5.159592360079138