Year	Number
1970	32.21196
1971	32.14084
1972	31.95253
1973	31.91023
1974	31.68302
1975	31.60505
1976	31.6027
1977	31.53306
1978	31.45451
1979	31.19698
1980	31.07397
1981	30.85779
1982	30.39871
1983	30.05102
1984	29.80052
1985	29.51561
1986	28.81998
1987	28.58377
1988	28.21245
1989	27.87392
1990	27.72323
1991	27.57741
1992	27.26188
1993	26.929
1994	26.50401
1995	26.30592
1996	26.11821
1997	25.90624
1998	26.16479
1999	26.54099
2000	26.01484
2001	25.07849
2002	24.64468
2003	24.29108
2004	24.36088
2005	24.04453
2006	24.21065
2007	24.51318
2008	24.14627
2009	23.99386
2010	23.65661
2011	23.25934
2012	22.72826
2013	22.72555
2014	22.41662
2015	22.15856
2016	21.99435
2017	21.7582
2018	21.69085