Year	Number
1974	24.4764
1975	23.58012
1976	22.11359
1977	21.32694
1978	20.1388
1979	19.29178
1980	20.93086
1981	21.91045
1982	21.55949
1983	20.81795
1984	20.85693
1985	21.54203
1986	20.9166
1987	17.16886
1988	16.12501
1989	17.46435
1990	18.19238
1999	19.61644
2000	19.1357
2001	18.56743
2002	18.60132
2003	17.68225
2004	18.78948
2005	18.80186
2006	17.36505
2007	17.68342
2008	17.41128
2009	18.27545
2011	18.66661
2012	17.8712
2013	17.52991
2014	15.81591
2015	16.61254
2016	16.97562
2017	15.63675
2018	16.01642
2019	15.17269