Year	Number
1973	29.29309
1974	29.14843
1975	26.84827
1976	26.97627
1977	27.43056
1978	26.99968
1979	28.09593
1980	29.20873
1981	27.95173
1982	26.6661
1983	26.40258
1984	26.1187
1985	25.8982
1986	26.18066
1987	25.66222
1988	26.12606
1989	25.89686
1990	24.68816
1991	25.21624
1992	26.69604
1993	27.42012
1994	28.00852
1995	28.07836
1996	28.41906
1997	27.66532
1998	26.5006
1999	25.60482
2000	24.84419
2001	24.2376
2002	22.89647
2003	21.82139
2004	20.58192
2005	19.79676
2006	21.64173
2007	20.77034
2008	20.17157
2009	20.48042
2010	21.62546
2011	21.36061
2012	21.73137
2013	21.1597
2014	19.72436
2015	18.97237
2016	18.42321
2017	17.62687
2018	17.18014