Year	Number
1970	35.005192108
1971	37.372101073
1972	39.7390100381
1973	42.1059190031
1974	44.4728279682
1975	46.8397369332
1976	47.9466943579
1977	49.0536517826
1978	50.1606092073
1979	51.2675666321
1980	52.3745240568
1981	53.2620283835
1982	54.1495327103
1983	55.037037037
1984	55.9245413638
1985	56.8120456906
1986	55.9494634822
1987	55.0868812738
1988	54.2242990654
1989	53.361716857
1990	52.4991346487
1991	49.4063689858
1992	46.3136033229
1993	45.9072343371
1994	45.5008653513
1995	45.0944963655
1996	44.6881273797
1997	44.2817583939
1998	43.5382485289
1999	42.7947386639
2000	42.0512287989
2001	41.3077189339
2002	40.5642090689
2003	40.7725856698
2004	40.9768085843
2005	41.183108342
2006	41.3894080997
2007	41.6060920734
2008	39.3215645552
2009	39.8407753548
2010	37.6254759432
2011	41.225337487
2012	39.7023191416
2013	38.9061959155
2014	36.7982000692
2015	36.1647628937
2016	35.6143994462
2017	34.8909657321
2018	33.2225683628
2019	31.0971928003
2020	30