Year	Number
1975	21.186440678
1976	21.7878622198
1977	22.3892837616
1978	22.9907053034
1979	23.5921268453
1980	24.1935483871
1981	24.8223072717
1982	25.4510661564
1983	26.079825041
1984	26.7085839256
1985	27.3373428103
1986	27.9661016949
1987	28.7588846364
1988	29.4696555495
1989	30.1804264625
1990	30.4811372335
1991	29.7977036632
1992	29.1142700929
1993	28.4308365227
1994	27.5130828712
1995	26.5953292197
1996	25.6775755682
1997	24.7598219167
1998	23.8420682653
1999	22.9243146138
2000	22.0065609623
2001	20.4951964383
2002	23.3324220886
2003	23.151995626
2004	22.9715691635
2005	22.7911427009
2006	22.6107162384
2007	22.4302897758
2008	21.9382176052
2009	25.1913613997
2010	27.4603608529
2011	30.1804264625
2012	34.8961180973
2013	28.2668124658
2014	29.6610169492
2015	31.7113176599
2016	29.7977036632
2017	29.5243302351
2018	28.2941498086
2019	31.5746309459
2020	37.5888463641