Year	Number
1973	24.08117
1974	23.91797
1975	23.97944
1976	23.57599
1977	23.46999
1978	23.5286
1979	23.39985
1980	23.13107
1981	23.33639
1982	22.92588
1983	22.7488
1984	22.6736
1985	23.08994
1986	21.20893
1987	21.34546
1988	21.32333
1989	21.20772
1990	21.42853
1991	22.28004
1992	21.42842
1993	20.65391
1994	19.16638
1995	20.74039
1996	20.12175
1997	18.84693
1998	18.48484
1999	18.17007
2000	17.95788
2001	17.9854
2002	17.92169
2003	18.0379
2004	17.57752
2005	17.55284
2006	17.70684
2007	17.85104
2008	17.03913
2009	16.11808
2010	15.33728
2011	16.23626
2012	16.41118
2013	15.81603
2014	15.70085
2015	15.36799
2016	15.84117
2017	14.74658
2018	15.1103