Year	Number
1971	13.80276
1972	14.38024
1975	16.51826
1976	20.84752
1977	19.40977
1978	15.14977
1979	21.32402
1999	22.93665
2000	23.88049
2001	24.02406
2002	23.96863
2003	24.80458
2004	23.24288
2005	22.40684
2006	21.53807
2007	20.54751
2008	18.95774
2009	17.14385
2010	16.23015
2011	14.75386
2012	14.40565
2013	13.1121
2014	12.2064
2015	11.44466
2016	10.66209
2017	10.13764
2018	9.75724