Year	Number
1970	19.469983775
1971	22.0930232558
1972	24.7160627366
1973	27.3391022174
1974	29.9621416982
1975	32.585181179
1976	32.585181179
1977	32.585181179
1978	32.585181179
1979	32.585181179
1980	32.585181179
1981	35.2893455922
1982	37.9935100054
1983	40.6976744186
1984	43.4018388318
1985	46.106003245
1986	41.1483684875
1987	36.1907337299
1988	31.2330989724
1989	33.1679728691
1990	35.1028467658
1991	33.6325412979
1992	32.1622358301
1993	30.6919303623
1994	29.2216248945
1995	27.7513194267
1996	26.2810139589
1997	24.8107084911
1998	23.382368848
1999	21.954029205
2000	20.5256895619
2001	19.0973499189
2002	17.6690102758
2003	17.4508743465
2004	17.2327384172
2005	17.0146024878
2006	16.0167658194
2007	15.0189291509
2008	18.8209843158
2009	17.8393726339
2010	21.8739859383
2011	23.409951325
2012	19.6998377501
2013	27.2850189292
2014	26.7495943753
2015	21.9524067063
2016	23.9858031368
2017	24.2238507301
2018	29.9031097891
2019	25.5704164413
2020	26.4042725798