Year	Number
1971	25.60292
1974	24.90108
1976	25.07663
1977	24.58569
1978	24.01408
1979	23.31022
1980	22.31237
1981	22.43252
1982	22.48166
1984	23.28318
1985	20.67081
1986	19.7973
1993	16.85776
1994	17.43521
2005	14.25797
2008	13.80388
2009	13.83706
2010	13.92133
2011	13.91457
2012	13.92234
2013	13.57944
2014	13.42901
2015	13.07852
2016	12.90002
2017	12.70365